Risk

Measles: An Old Bad Disease Returns

FEB 28, 2026

Epidemiology of Measles

Measles is the world’s most infectious disease. It has a basic reproductive number (R₀) of 12-18. That means that each infected person infects 12-18 other non immune people. As a result, 90% of susceptible people will get measles from exposure to 1 person with measles. The measles virus can linger in the air for 2 hours after a person with measles has left a room. Any susceptible person who enters that room during the 2 hour time period can be infected with measles. Here is a picture of a child with a typical measles rash.

Most US doctors have never seen a case of measles like this child. That, unfortunately is about to change.

For comparison of infectivity let’s look at the R₀ for other diseases we consider very contagious. R₀ for Ebola is 1.5-2.5, R₀ for COVID is 2.2-3.6 and R₀ for influenza is 1.2-1.4. As you can see none of these diseases comes even close to being as infectious as measles.

There are only two other diseases that are closer to being as contagious as measles. The R₀ for pertussis (whooping cough) is 5-17 (see my recent post on pertussis). The R₀ for varicella (chicken pox) is 10-12.

History of Measles in the US Prior to Measles Vaccine

Prior to the introduction of the measles vaccine in 1963, virtually all children in the US had measles by age 15. Having measles (and surviving it) provides lifetime immunity to measles, so adults born before 1954 have had measles and are already immune. People born before 1954 do not need to be vaccinated for measles.

Symptoms of Measles

Here is a description of measles symptoms from the Mayo Clinic

“Measles symptoms show up around 7 to 14 days after contact with the virus.

The first symptoms usually are:

Fever, which may be as high as 105 degrees Fahrenheit (40.6 degrees Celsius).
Dry cough.
Runny nose.
Red, watering eyes, called conjunctivitis.

About 2 to 3 days after the first symptoms, you also may see tiny white spots inside the mouth, called Koplik spots.

About 3 to 5 days after symptoms first start, or about 14 days after you come into contact with the virus, it’s common to see a rash. The rash is made up of large, flat spots and small raised bumps. The rash starts on the face or neck and spreads down the body from the chest to the arms and legs. A person with measles can spread the virus four days before the rash appears and four days after.”

Measles is obviously not a pleasant disease to have. Fever of 104-105 is pretty scary. All children with measles are miserable, but most children without complications recover from measles in about 10 days.

Complications of Measles

This information comes from the CDC.

Ear Infections

1 in 10 children with measles get bacterial ear infections that may need antibiotics

Hospitalization

About one in 5 children and adults with measles have to be hospitalized,

Pneumonia

One out of every 20 children with measles gets measles pneumonia. pneumonia is the most common cause of death from measles in children.

Encephalitis

One child out of every 1000 will develop encephalitis (inflammation of the brain). This condition can also cause death, but children who survive may have deafness and/or intellectual disability.

Death

Three children out of every 1000 children with measles will die from their disease, either from respiratory or neurological complications.

Subacute Sclerosing Pan Encephalitis (SSPE)

This is a uniformly fatal brain disease that can occur 7-10 years after a measles infection. Fortunately it is rare, but children who get measles before age 2 are at higher risk of SSPE.

Herd Immunity to Measles

The recommended regimen for MMR (measles, mumps and rubella) vaccination that gives the most protection is to be vaccinated at age 1 year and a second dose at age 4-5. This regimen gives lifelong 97% protection against contracting measles. This means that children under 1 year of age are protected only by everyone around them being immune to measles. Measles is a live vaccine (a weakened strain of the measles virus). People who have weakened immune systems because of chemotherapy or other causes of immune deficiency cannot receive live virus vaccines. Their only protection from measles is herd immunity. Herd immunity means that enough people are vaccinated or immune that a susceptible person who cannot be vaccinated is protected by the “herd” of people who are vaccinated.

Measles is so contagious that 95% vaccination rate is necessary to prevent measles entirely. Outbreaks start to occur if vaccination rates fall below 95%. Large outbreaks occur at vaccination rates below 90%.

In 2025 MMR vaccination rates ranged from a low of 75% in Idaho to 98% in Connecticut. Only 10 states had MMR vaccination rates above 95%.

MMR Side Effects

There are occasional side effects to MMR vaccine but the vast majority of those are mild. They include pain and swelling at the injection site, fever, a mild rash about 10 days after vaccination and some joint stiffness. When they happen these side effects disappear completely in a day or two. There are some very rare more serious reactions including febrile seizures (8 in 10,000 vaccinations), bruising or bleeding from low blood platelets (1 in 20,000 vaccinations) and severe allergic reactions (1 in 1 million vaccinations. Febrile seizure is scary for parents but does not recur and has no long term effects on the child. The other rare side effects are manageable. There are no known deaths from side effects of MMR vaccine. It is also important to point out that all of these side effects are much more common with measles infections.

MMR Vaccination Resistance

Worry about side effects of MMR vaccine has led to parents refusing MMR for their children. The main reason for vaccination resistance is worry that MMR vaccine causes autism. Very large well designed research studies have shown definitively that there is no connection between MMR vaccine and autism. The misinformation about MMR vaccine and autism unfortunately persists. This vaccination resistance has decreased the vaccination rate below the 90% threshold for serious outbreaks of measles in large parts of the US.

Current Outbreaks of Measles

I think the best way to show the resurgence of measles in the US is graphically. Below is a graph from the Johns Hopkins Bloomberg School of Public Health.

As you can see from this graph, measles cases started to rise after 2019 and went through the roof in 2025. 2026 is on track to have even more cases than 2025.

Deaths from Measles

Worldwide in 2025 95,000 children died from measles almost entirely from lack of measles vaccination. Three of those deaths were in the US. Given the resurgence of measles outbreaks across the US, we will undoubtedly see more deaths from measles.

Bottom Line

Measles is the most contagious disease in the world. Most children recover, but complications occur in 20% (one in five) children with measles. Complications include ear infections, hospitalizations, pneumonia, encephalitis and death. Vaccination rates must be at least 95% for complete herd immunity. Once vaccination rates fall below 90% large outbreaks of measles occur Vaccination rates are below 90% for large parts of the country and large outbreaks continue to occur in those communities with low vaccination rates. Measles is back with a vengeance!

Pertussis (Whooping Cough): Resurgence of a Deadly Disease

A recent article in the journal Pediatrics reported a surge in cases of pertussis, commonly known as whooping cough. Unfortunately the article is only available to subscribers to the journal. Here is a link to a description of that article in a medical news service called Medscape. Pertussis is a bad disease. See below.

History of pertussis

Pertussis is caused by a bacterium, Bordatella Pertussis. Prior to the advent of pertussis vaccines, pertussis was one of the leading US causes of death of children under 5 years of age. There were over 200,00 cases and 9000 childhood deaths in the US from pertussis every year (a rate of 4.5 deaths per thousand children). Pertussis was especially lethal in infants, and was probably the leading cause of death in this age group. Worldwide, pertussis prior to vaccines was just as bad as in the US or worse. Worldwide there were 24.1 million cases and 160,700 deaths in children under five every year.

Epidemiology of pertussis

In un-immunized people pertussis is extremely infectious, almost as much as measles. One infected person on average infects 12-18 other people. In adolescents and adults pertussis is unlikely to cause death or hospitalization, but it is an extremely unpleasant disease. Older children and adults have paroxysms of coughing, followed by a loud, wheezing inspiration (the whoop of whooping cough). These symptoms can last for weeks or months. The coughing is sometimes so severe that people break ribs or develop hernias. Treatment with antibiotics is used to prevent transmission. Antibiotics are also given to contacts to prevent them from getting infected. Antibiotics do not have any effect on the length or severity of the disease. Those who have symptomatic pertussis just have to wait for it to go away. Here is an audio file of a child with pertussis. You should listen to it realize what a severe disease pertussis is. Let me warn you that it is distressing to listen to.

Pertussis vaccines

Whole cell pertussis vaccines

Whole cell pertussis vaccine combined with vaccines for tetanus and diphtheria was widely introduced and given to infants and children in the 1940’s. This was a highly effective vaccine. It not only prevented disease, but also prevented colonization and therefore stopped transmission of pertussis. It reduced the cases of pertussis by 75%. Unfortunately, the whole cell vaccine had rare but concerning side effects.These iincluded persistent crying, febrile seizures and hypotonic-hypoeresponive episodes (HHE). Children with HHE had sudden onset of reduced muscle tone, decreased responsiveness to verbal or other stimuli, and change in skin color (pallor or cyanosis) that occurred shortly after vaccination. These adverse events, though temporary were obviously distressing to parents. There were also rare cases of encephalopathy (Inflammation of the brain) that caused permanent disability. These cases were so rare that it was impossible to know whether these permanent disabilities were caused by the vaccine, or were simply associated but not causal. Controversy over whether the vaccine had any role in these cases continues even today.

Acellular pertussis vaccine

Because of the rare but distressing side effects of whole cell pertussis vaccine, a new vaccine was developed that had components of the pertussis bacterium, but not whole cells. This was called the acellular vaccine. This acellular vaccine had far fewer and milder adverse reactions than the whole cell vaccine. The combination vaccine is abbreviated DTaP (diptheria-tetanus-acellular pertussis). This is the vaccine used for children today. Unfortunately the acellular pertussis vaccine is less effective than the previous whole cell vaccine. It does prevent children from getting ill with pertussis, but it does not prevent colonization of the nose and throat. Children who are colonized in this way are not sick, but they are infectious and can pass on the virus to other children and adults. This keeps the bordatella pertussis bacteria circulating in communities.

Waning Immunity

Neither the whole cell nor the acellular vaccine provides lifetime immunity, unlike the Measles-Mumps-Rubella vaccines, which do provide lifetime immunity. Even people who have pertussis do not get lifetime immunity. Immunity from vaccines and infection wane over time. It appears that the acellular pertussis vaccine gives good protection from getting sick from pertussis for about 4 years, and starts to wane after that. The result is that we still see pertussis even in fully immunized children and adults starting about 5 years after the last routine immunization, which occurs at between 4 and 6 years of age. A booster TDaP is also recommended at around 12 years of age. This means that the most vulnerable children, that is children 5 or under are protected from getting ill from pertussis. Infants below 2 months of age (too early for vaccination) are protected by the recommendation that all pregnant women get a booster TDaP vaccine in the third trimester of every pregnancy. Anyone who is going to have extended contact with an infant under 2 months should also get a booster TDaP.

Risk of resurgence of severe pertussis

Bordatella pertussis continues to circulate in communities because of colonization of immunized children. Resistance to vaccinating children with DTap can quickly cause a resurgence of pertussis in infants and young children. This would be disastrous and is already happening. In 2024, there were 35,435 documented cases of pertussis across the U.S., including 655 in Colorado. That was a huge jump over the 7063 cases in all of 2023. Large states, including New York and California, logged high numbers of pertussis infections in 2024. So did some less-populated states like Idaho, Washington and Oregon, each of which reported more than 1,000 cases of pertussis. There were 10 deaths from pertussis in 2024. Cases are on track to be even higher in 2025.

Research on new pertussis vaccines

The search is on for a new pertussis vaccine that prevents colonization but that also does not cause the distressing side effects that happened with the whole cell pertussis vaccine. The best candidate at the moment is a live vaccine that has been genetically modified to eliminate the toxins produced by the bacterium. If and when approved this vaccine will be administered nasally. In rhesus monkeys it prevented colonization with bordatella pertussis and had no significant side effects. It is currently in phase 3 trials in humans.

Bottom Line

Pertussis is a serious disease and is life threatening to infants and young children. The severity and duration of pertussis are not affected by antibiotics that are given to limit the spread of the disease. The only effective treatment of pertussis is prevention through immunization. Acellular pertussis vaccine is much safer but also less effective than the old whole cell vaccine. It allows bordatella pertussis to continue to circulate in communities. Resistance to immunization of children has led to a marked increase in serious pertussis infections in 2024 with 10 deaths reported. Pertussis cases are on track to be even higher in 2025. A promising new attenuated live pertussis vaccine is in phase 3 trials and may soon be approved assuming research funding is not withheld by the Trump administration.

Autism: Is There An Epidemic?

HHS Secretary Robert F. Kennedy Jr has declared that there is an epidemic of autism and that there must be some environmental toxin that is causing it. The evidence says otherwise. I will review the evidence in this post.

Increased diagnosis of autism

There is no question that autism is being diagnosed more frequently than in the past. According to the CDC, in 2000 the prevalence of autism was 7 per thousand 8 year old’s and by 2024 was 32 per thousand, a 4.5 times increase.

Evolution of diagnostic criteria for autism

Up until 1980, autism was considered a form of schizophrenia in children. It was thought to be rare, probably because many of these children were institutionalized. Over the various versions of the DSM (Diagnostic and Statistical Manual) criteria over the years, the criteria to diagnose autism have been constantly expanded, resulting in a progressive increase in the frequency of the diagnosis of autism. In the most recent version of the DSM all the subcategories of autism including Asperger’s disease were combined into one diagnosis – autism spectrum disorder. This resulted in a marked increase in the diagnosis of autism, because it included all the less severe forms of autism. There is an excellent description of this evolution on the Arizona Autism United blog: How the Autism Diagnosis Has Evolved Over Time.

Has the frequency of severe autism increased?

Severe or profound autism includes children who have no or little speech, are intellectually disabled, and some have challenging behavior that interferes with safety and well being. According to the CDC, people with severe autism make up about 26% of people with autism. Kennedy says that severe autism has markedly increased. According to Christine Ladd-Acosta, who is the vice director of the Wendy Klag Center for Autism and Developmental Disabilities, the data show that severe or profound autism has increased little or none in the last 10 years. Maureen Durkin, another well known autism researcher, divided autism cases up into different buckets. She found that severe autism has not increased at all, and in fact has decreased a little.

Screening for autism spectrum disorder

The American Academy of Pediatrics began recommending screening children for autism spectrum disorder in 2006. Screening is recommended at well child visits. There is some controversy about the benefits of screening children with no symptoms, but it is clear that screening has increased the diagnosis of autism spectrum disorder, especially milder forms of autism. Screening has also resulted in earlier diagnosis of children with more severe autism. Earlier intervention improves the outcomes in these children.

Causes of Autism Spectrum Disorder

Genetic Causes

Multiple studies including identical twin studies have shown the cause of 80% of autism spectrum disorder cases are genetic. Here is a link to an NIH article that summarizes these studies. Genetic causes are both hereditary and caused by genetic mutations.

Environmental causes

There are certain environmental factors associated with slightly increased risk of autism spectrum disorder. All of these factors account for a very small increase in the incidence of autism spectrum disorder, each less than 1%.

Advanced parental age
Prenatal exposure to air pollution or certain pesticides
Maternal obesity, diabetes or immune system disorders
Extreme prematurity or very low birth weight
Birth complications leading to periods of oxygen deprivation to the baby’s brain

Do childhood vaccines cause autism spectrum disorder?

The answer to this is a definite no. Multiple large well designed studies have shown no association of vaccines, or any component of vaccines including thimersal and aluminum that have any association with autism spectrum disorder. Here is a link to an article from the CDC summarizing these studies.

Does taking Tylenol (acetaminophen) during pregnancy cause autism?

Once again the answer is no. There were a few small studies that showed an association of acetaminophen during pregnancy and development of autism spectrum disorder. Larger, better designed studies have shown no association of acetaminophen use during pregnancy and subsequent development of autism spectrum disorder in children born from those pregnancies.

Autism spectrum as neurodiversity

Many people with milder forms of autism spectrum are fully functional and live independently. They view themselves as on a spectrum of neurodiversity rather than having a disorder. Here is a link to an article from Autism Speaks describing the idea of neurodiversity.

Bottom Line

The increase in the incidence of autism spectrum disorder is almost entirely due to increased diagnosis and increased awareness. The cause of 80% of autism spectrum disorder is genetic. There are a few environmental causes that have increased over time, but these account for only a tiny portion of the increase. There are many well designed studies that show that vaccines do not cause autism spectrum disorder. There are also similar large well designed studies that show that taking acetaminophen during pregnancy does not cause autism spectrum disorder in the babies born from those pregnancies.

Many people on the autism spectrum are fully functional and live independently. They view themselves as people with neurodiversity rather than people with a medical disorder.

There is a very good podcast called Science Versus that reviews all of the evidence that I have outlined above. It is worth listening to. Here is a link to the transcript of the podcast. You can listen to the episode on your normal podcast app. The show notes for the episode has all the references that are used in the episode.

Water Fluoridation

This is another post responding to misinformation promulgated by HHS Secretary Robert Kennedy Jr. Misinformation seems to proliferate faster that true science-based information. Perhaps one way to combat this is for readers of these blog posts to share them as widely as possible to people they know.

Secretary Kennedy is opposed to adding fluoride to public water supplies. He maintains that adding fluoride to public water supplies causes lower IQ’s in children. Two states, Utah and now Florida have already banned fluoridation of public water supplies, mostly in response to his claims about the evils of water fluoridation. I will examine the evidence for these claims in this post

Positive effects of water fluoridation

The US Public Health Service recommends public water fluoridation at a level of 0.7 mg per liter. This level of fluoride in water reduces tooth decay in children by 25% even in children who do not brush or floss regularly. This therefore most benefits poor and marginalized populations for whom dental hygiene can be difficult. Public water fluoridation at this level is one of the most effective public health interventions. Tooth decay can lead to chronic inflammation, which can lead to many other diseases including heart disease.

Sources of natural fluoride

Fluoride occurs naturally in almost all water supplies through the erosion of rocks and soil containing fluoride. The levels of natural fluoride are usually too low to prevent tooth decay, but some water supplies have much higher levels of natural fluoride up to as much as 50 mg per liter in some mountainous and volcanic regions.

Adverse effects of high natural fluoride

Fluorosis

Fluorosis has two components. At fluoride levels greater than 1.5 mg/L children who have growing teeth can develop brown discoloration of teeth. This is called dental fluorosis and is mostly a cosmetic problem. Long term exposure to fluoride levels greater than 10 mg/L can lead to skeletal fluorosis, which is a much more serious condition. In skeletal fluorosis the bones are generally weaker than normal with stiffness and pain in the joints as the early symptoms. In severe cases, muscles are impaired and bones in the central skeleton are irregularly thickened.

Lower IQ in children

In January of 2025 JAMA (Journal of the American Medical Association) published an analysis of combined data from many international studies that showed lower IQ scores in children exposed to higher levels of fluoride from all sources: Fluoride Exposure and Children’s IQ Scores. The study found that the higher the exposure to fluoride, the lower were the children’s IQ scores. This finding was statistically significant for levels above 1.5 mg/L but not at or below this level. None of these studies were done in the United States. The US Public Health recommendation of 0.7 mg/L is well below the threshold for association of lower IQ in children.

Other sources of fluoride

The most significant other sources of fluoride are supplements, toothpaste and oral rinses. For children who have fluoride at 0.7 mg\l in drinking water, fluoride containing supplements should not be given. Most toothpastes contain fluoride, so children with fluoride in the water supply should use only a pea sized amount of toothpaste per brushing and should be encouraged to spit out the toothpaste after brushing. If the water supply has not been fluoridated and contains only trace amounts of natural fluoride, then supplements should be given to children.

Bottom Line

Fluoridation of public water systems at the recommended concentration of 0.7 mg/L is safe and effective at markedly reducing tooth decay in children. There is no evidence that fluoride in water at this level has any adverse effects. There is some evidence that concentrations of higher than 1.5 mg/L are associated with modest decreased IQ in children. Elimination of fluoride from public water systems will increase tooth decay in the most vulnerable populations and will not have any benefit. Children who live in communities with fluoridated water should not take fluoride supplements, should use only small amounts of fluoridated toothpaste, and should be encouraged to spit out toothpaste after brushing and not swallow it. Communities who have high natural levels of fluoride in drinking water can reduce fluoride to safe levels by reverse osmosis or charcoal filter systems.

MMR Vaccine Risks in Perspective

This post is a follow-up to my recent post about measles and MMR vaccine. The purpose of this post is to compare the risk of adverse effects from the MMR vaccine to other risks that we take with our children every day.

Annual Deaths of children under 18

In the US 37,000 children under the age of 18 die every year. In 2022, the last year for which we have complete data, 604 children were killed in automobile accidents. This figure includes those killed as passengers, walking to school or in their neighborhoods, or riding their bicycles. Here is a table from the New England Journal of Medicine showing the most common causes of death of children since 1999.

As you can see from the graph, motor vehicle deaths of children have gone down significantly since 1999, but are still the second leading cause of death in children. Firearm injuries have now surpassed motor vehicle deaths as the leading cause of death in children.

All of these risks are small, the highest being 4.5 deaths per 100,000 Children. These are risks we take with our children every day. There is a risk when they ride in your car. There is a risk when they walk in their neighborhoods. There is a risk when they ride their bicycles. There is a risk that they will be killed by a mass murderer when they go to school. The risks of adverse reactions to vaccines are actually lower than the risks that we take with our children every day. Adverse reactions to vaccines almost never kill children

Deaths of children due to MMR vaccine

There have been only two documented deaths due to MMR vaccine in the 62 years it has been available. Both of these deaths were in children with Severe Combined Immunodeficiency Syndrome (SCIDS). You may remember a movie about a child with this syndrome. It was called “The Boy in the Bubble.” These children should never have received a live virus vaccine, such as MMR.

MMR Vaccine and Autism

Robert F. Kennedy Jr, the current head of HHS, has contended that MMR vaccine causes autism. There was a paper published by Andrew Wakefield in the medical journal, the Lancet, that studied 12 children and concluded that MMR vaccine was linked to autism. It was later discovered that he had falsified his results and the paper was retracted by the Lancet. This discredited paper, plus another one by the same author are still cited by people, including our current head of HHS, as evidence that MMR vaccine causes autism.

Study by Brent and Taylor

Brent and Taylor and colleagues examined the records of 498 children with autism. Cases were identified before and after MMR vaccine became available in the UK. They compared the incidence of autism in vaccinated and unvaccinated children and found no difference.

Study by Madsden and Colleagues

Madsden and colleagues did one one of the best and most rigorous studies. The study included 537,303 children representing 2,129,864 person-years of study. Approximately 82% of children had received the MMR vaccine. The risk of autism in the group of vaccinated children was the same as that in unvaccinated children. Furthermore, there was no association between the age at the time of vaccination, the time since vaccination, or the date of vaccination and the development of autism.

Other studies

Many other well designed studies have shown no association between the MMR vaccine and autism.

Bottom Line

We daily accept small risks of injury and death of our children. There are no activities involving children that are without some risk. The risks of MMR vaccine side effects (or any other vaccine) are no larger than the risks we take with our children every day. See my last post for a list of possible side effects of MMR vaccine. Severe side effects of MMR vaccine are very rare. When given appropriately to children with normal immune systems, death is not one of the risks. The one study by Andrew Wakefield that showed a connection with MMR vaccine and autism was shown to be fraudulent and was retracted. Multiple well designed studies have definitively shown that MMR vaccine does not cause autism.

Inflammation: Pathway to Chronic Diseases

Inflammation is activation of the immune system in response to threat or injury to the body. Acute inflammation mobilizes the immune system to repair an injury or fight an infection. Once healing takes place the immune system goes back to baseline. Chronic inflammation, however, involves long term activation of the immune system caused by some ongoing stress to the body. More and more, researchers are beginning to show that chronic inflammation is the common pathway to many diseases. There are multiple causes of chronic inflammation. In this post I will write about the causes of chronic inflammation. I will also do a series of posts about the many diseases that chronic inflammation causes. These posts will be based on the structure of an excellent book: Inflamed – Deep Medicine and the Anatomy of Injustice. It is not easy to read because it is disturbing but I highly recommend it. I will also write about a test to measure chronic inflammation. I will write about things you can do to decrease chronic inflammation if you have it and how to prevent it if you don’t. There are many causes of chronic inflammation that have to do with the structure of our society. These are things an individual cannot control. These societal causes will take ongoing efforts by all of us to change some of the toxic structures of society.

The Process of Inflammation

The inflammatory process starts with damage or threat of damage to the body. That can be an infection, a wound, or perceived threat of such. The immune system mobilizes white blood cells called macrophages to the injured area or site of infection. The cells of the immune system also release a cascade of messenger molecules called cytokines that amplify inflammation. These include interleukin 1ß, interleukin- 6 and tumor necrosis factor -α. The liver also releases a protein called c-reactive protein. When the threat is neutralized the immune system helps the body start to heal by releasing anti-inflammatory cytokines including interleukin (IL)-1 receptor antagonist, IL-4, IL-10, IL-11, and IL-13.

In chronic inflammation the pro-inflammatory cytokines continue to predominate and the c-reactive protein continues to be elevated.

Causes of Chronic Inflammation

Causes an individual can do something about

Low levels of physical activity.
Having a BMI at or above 30 , especially when excess weight is deep within your belly (visceral fat). The best way to measure belly fat is to use a tape measure to measure your waist at the widest point. Increased belly fat is greater than 35 inches for women or greater than 40 inches for men
An imbalance of healthy and unhealthy bacteria in your intestine (dysbiosis). Dysbiosis can be caused by antibiotics and by eating foods low in soluble fiber.
Regularly eating foods that cause inflammation, especially highly processed foods, or foods high in sugar or salt
Inadequate sleep
Using tobacco products.
Regularly drinking too much alcohol
Periodontal disease (gum infection) and tooth decay
Perceived stress

Societal Causes

Experience of racism (structural or personal)
Poverty
Homelessness
Worry about debt
Work stress
Exposure to air pollution
Exposure to chemicals (pesticides and herbicides for farm workers, glyphosphate (RoundUp) for everyone, microplastics in our bloodstreams for everyone. Every day, we are surrounded by thousands of synthetic chemicals. They are in our food, clothes, tools, furniture, toys, cosmetics and medicines. We know the health effects of only a few of these).

Diseases caused by chronic inflammation

Cardiovascular Disease (coronary artery disease, heart attacks, congestive heart failure)
Strokes
Type 2 diabetes
Cancer (multiple types)
Inflammatory bowel disease (crohns disease, ulcerative colitis)
Rheumatoid Arthritis
Lupus and similar autoimmune diseases
Asthma
COPD
Pulmonary fibrosis
Depression

Tests to measure chronic inflammation

All of the inflammatory cytokines can be measured but those are expensive tests. A simple inexpensive test that measures inflammation, both acute and chronic is high sensitivity CRP. It will also be high with an acute infection or injury, but will return to normal after the infection or injury have resolved. If it remains elevated when you are not sick or injured it is a sign of chronic inflammation. It may be worth asking your doctor to order this test if you have any of the individual or societal risk factors for chronic inflammation. A normal hs-CRP is less than 0.55 mg/dl in men and less than 1.0 mg/dl in women. If your hs-CRP is high in the absence of acute infection or injury, that can serve as motivation to make lifestyle changes to decrease your chronic inflammation and put you in a population that has less risk of developing any of the diseases associated with chronic inflammation.

Anti-inflammatory lifestyle

Exercise regularly. The CDC recommends 30 minutes of moderate exercise (walking briskly) for 30 minutes at least 5 days a week.
Eat mostly unprocessed or minimally processed foods and avoid sugary drinks or foods with added sugar or high fructose corn syrup. Also include foods with high soluble fiber such as beans, carrots, sweet potatoes, nuts, berries and most fruits (not fruit juice). Organic foods, while more expensive, have no residual pesticides or herbicides. If you eat meat buy grass fed beef, and pasture raised chicken and pork. Eat more plant-based foods than meat.
Avoid taking antibiotics as much as possible
Sleep. Average at least 8 hours a night
Floss your teeth daily, brush twice a day and see your dentist every 6 months
If you don’t smoke, don’t start and if you do smoke quit.
It is better not to drink alcohol at all, but if you do limit it to 1 drink a day or less.
Learn meditation or self hypnosis to manage stress. There are good books and videos, but an in person course is best if it is available.
Drink only filtered water and not bottled water in plastic bottles
Gas stoves cause significant indoor air pollution. If possible switch to an electric stove. Induction type burners actually heat more quickly than gas. If you have to use a gas stove, be sure to turn the ventilator fan on and open a window if possible.

Bottom Line

Treatment

Malaria can be treated successfully with several different drugs depending on the type and resistance. There are drugs that travelers can take if they are traveling to an area where malaria is present that will prevent infection. The newest development is a malaria vaccine that can be given to children in endemic malaria regions.

Who is at risk?

There is virtually no local transmission of malaria in the US in modern times. In a typical year, the U.S. reports about 2,000 cases of malaria, almost all of which are in travelers who have been to an endemic region. Malaria occurs only in tropical regions and below 6,500 feet above sea level. Most cases of malaria occur in sub-Saharan Africa, but it also occurs in parts of Oceania (such as Papua New Guinea) and in parts of Central and South America and Southeast Asia. Worldwide, malaria has caused 608,000 deaths in the past year. Malaria is one of the world’s most severe public health problems, with nearly half of the world’s population at risk for infection.

How to prevent mosquito bites.

Indoors

Make sure all windows have screens and any holes in the screens are patched. Use air conditioning if you have it during the spring and summer when mosquitos are most active.

Outdoors

Mosquitos lay eggs in standing water. Remove or empty any receptacles outside that allow water to pool such as saucers under flower pots. Tightly cover any water storage containers. If you have a birdbath, use a battery or solar powered agitator. Mosquitos only lay eggs in still water.

Residential outdoor misting systems that use permethrin provide good mosquito control and are safe for humans, birds and animals. They are somewhat expensive, however.

Use an EPA-registered insect repellant with one of the following ingredients:

DEET (Has been shown to be non-toxic for humans and repels but does not kill insects)
Picaridin (known as KBR 3023 and icaridin outside the United States)
IR3535
Oil of lemon eucalyptus (OLE)—A plant-derived ingredient (must be applied more frequently than DEET)
Para-menthane-diol (PMD)
2-undecanone—A plant-derived ingredient

Wear loose long sleeved shirts and long pants when outside when mosquitos are active

Treat items such as boots, pants, socks, and tents with permethrin or buy permethrin-treated clothing and gear.

Bottom Line

Mosquitos transmit many diseases, but all of these are quite rare in the US. Global warming may well increase mosquito transmitted diseases in the US in the future. The vast majority of mosquito bites in the US are just a nuisance and do not transmit disease. In other parts of the world mosquito disease transmission is a major public health problem. Travelers to areas where mosquito borne diseases are prevalent should use mosquito bite prevention strategies, especially EPA-approved insect repellents. Travelers to areas endemic for yellow fever should be vaccinated prior to travel. Travelers to malaria prevalent regions should start preventive medicine 1 week before and continue 1 week after travel.

Health Effects of Social Drinking: Risks and Impacts

Humans have been drinking beverages containing alcohol for well over a thousand years. Mild to moderate acute alcohol intake has a euphoric effect probably caused by release of dopamine in the brain. At lower blood levels alcohol promotes social interaction, which is likely why it has such a long history of use in human society. The actual effect of alcohol on the brain is complex and not well understood. Brain function is a delicate balance of excitatory and inhibitory neurotransmitters. Alcohol alters this balance in a complex way that is difficult to measure and characterize.

Addiction to alcohol occurs in some people. About half of alcohol addiction is genetically determined. Other causes include use to alleviate mental disorders such as anxiety or depression or psychosocial stress. Physicians used to use the term alcoholism to refer to alcohol addiction, but now the correct term is alcohol use disorder. This can range from mild to severe and is defined by NIH as a medical condition characterized by an impaired ability to stop or control alcohol use despite adverse social, occupational, or health consequences. Severe alcohol use disorder has major health and social consequences for both individuals and society.

In this post I’m not going to write further about alcohol use disorder. That is a subject unto itself. Instead I’m going to focus this post on the health effects of alcohol use that does not meet the definition of alcohol use disorder, so called “social drinking.”

Physicians used to say that a safe level of alcohol use was 2 drinks a day for a male and 1 drink a day for a female. Now physician advice is that no level of alcohol use is safe. Alcohol use has been shown to increase the risk of many cancers as well as heart disease. The real question is how big is the risk for these conditions and at what level of alcohol intake.

Measuring alcohol use

The term “drink” is not very precise. I once had a patient who insisted she only had one drink a day. Her one drink consisted of a 12 ounce glass of vodka. The UK has developed a different measure of alcohol intake called units of alcohol. One unit of alcohol is the amount an average person can metabolize completely in 1 hour. That amount is 10 cc (1/3 of an ounce) or 8 grams of pure alcohol. Here is a list of the number of units in beer, wine and cocktails:

Four ounce glass of wine (red or white) – 1.5 units
Six ounce glass of wine (red or white) – 2.1 units
Eight ounce glass of wine (red or white) – 3 units
Low alcohol pint of beer – 2 units
High alcohol pint of beer – 3 units
Bottle of beer – 1.7 units
Cocktails – 2.5-3 units

If you drink alcohol, add up the number of units you drink per week. The greater the number of units per week, the higher the risk, which I will quantify below. Be aware that most of these risks are very small. There are quite a few people who don’t drink at all or drink only rarely. These people simply don’t have any desire to drink alcohol or don’t like the way it makes them feel. These essentially non-drinkers form the comparison group for the risk of drinking alcoholic beverages.

Risk of Alcohol Use Disorder

The vast majority of social drinkers do not develop alcohol use disorder, but people who have a family history of alcohol use disorder are at greater risk if they start social drinking. Social drinking is also not a good idea for people with severe anxiety or depression.

Risk of Cancer

Drinking alcohol increases the risk of certain cancers, particularly colorectal cancer, breast cancer, liver cancer, esophageal cancer, and throat cancer. The total absolute cancer risk for drinking greater than 14 units of alcohol per week from age 25 to 85 is 4% for men and 5.4% for women. That translates to an annual risk of .0667% for men and .09% for women. To put that risk in perspective, the annual risk of death from a car accident in the US is .013%. and the annual injury risk from a car accident is 1%.

Risk of Death

In a large study in the UK, risk of death from all causes was associated only with drinking more than 42 units of alcohol per week.

Accelerated Ageing

Recent studies have looked at two measures of biologic ageing. At the end of each chromosome are structures called telomeres. It is known that these telomeres shorten as a person ages. The other measure is called epigenetics. These are non-DNA changes that are heritable. Some of these epigenetic changes increase as a person ages. Recent studies show an association between alcohol intake and these biologic ageing changes. There seems to be a dose response relationship. The more alcohol you drink, particularly liquor as opposed to beer and wine, the more your telomeres shorten and epigenetic changes accumulate. This association was most marked in people with alcohol use disorder. There was little association for light to moderate social drinkers. Association does not mean causation, however the researchers controlled for other things that might account for these changes like smoking, diabetes, and others. It is possible and even likely that these ageing changes were caused by alcohol intake.

Risk of Accidents

Even mild to moderate drinking impairs reaction time so driving after drinking any amount of alcohol is not a good idea. Heavier drinking causes more impairment of motor function and increases risk of accidents such as falls. Driving after heavier drinking markedly increases the risk of auto accidents, which can injure or kill others as well as the one who is drinking. Anyone who drinks any amount of alcohol outside the home should have a designated driver who agrees not to drink, or call Uber, Lift, or a taxi to be driven home.

Sleep Disturbance

Drinking alcohol, particularly later in the evening can cause sleep disturbance with early awakening and difficult getting back to sleep. This can occur even with light to moderate drinking.

Bottom Line

Drinking alcohol at all does increase the risk of cancer and heart disease. The annual risk is dose related, but is still very small for light and moderate drinkers (14-21 units per week) The risk of illness and death and accelerated ageing is higher for heavier drinkers, but still relatively small. Drinking alcohol later in the evening often causes sleep disturbance. This can usually be avoided by timing drinking alcohol in the late afternoon or early evening. The risk of cancer and heart disease from drinking is low but not zero. People who choose to drink alcohol are accepting that risk. Driving is not a good idea for any level of alcohol intake. Light to moderate drinking is definitely less risky than heavier drinking, which includes association with accelerated ageing as well as increased risk of auto accidents. These risks are still fairly small. People who have alcohol use disorder should seek professional help and strive to be completely abstinent from alcohol.

Osteoarthritis: Understanding Risk Factors & Effective Management

According to the World Health Organization as of 2019, 528 million people world wide were living with osteoarthritis, a more than one hundred percent increase since 1990. Osteoarthritis is the most common type of arthritis, affecting primarily the knees, hips, hands and spine. In this post I will write about the risk factors for developing osteoarthritis, both the ones you can’t do anything about and the things you can do to reduce your risk of developing osteoarthritis. Since osteoarthritis is so common, I will also write about the best way to manage osteoarthritis if you already have it.

Risk factors you can’t modify

Age

73% of people with osteoarthritis are over 55. The risk of osteoarthritis increases with increasing age. According to data from the CDC, osteoarthritis occurs in 3.6% in adults ages 18–34 to 53.9% in those age 75 and older.

Gender

The CDC estimates that about 1 in 4 women have been diagnosed with osteoarthritis, compared to about 1 in 5 men. The percentage of women with osteoarthritis increases after menopause. For example, among people aged 40–49, about 10% of women and 7% of men have knee osteoarthritis, but between the ages of 60–69, that prevalence rises to 35% in women and 19% in men.

Genetics

There is no gene for osteoarthritis. The genetic risk of osteoarthritis is the result of many genes, each contributing only a small amount of risk. The total genetic contribution to osteoarthritis is about 30%. In other words a little less than a third of cases of osteoarthritis are due to genetic factors.

History of joint trauma or injury

Any injury to a joint or a fracture involving a joint increases the risk of post traumatic osteoarthritis. For example the incidence of arthritis of the knee after ACL tears is as high as 60%.

Risk factors you can modify

Obesity

Maintaining the lowest weight that is practical for you reduces your risk of developing osteoarthritis of the hip and knee. Obesity markedly increased the risk of developing osteoarthritis and also serves as a multiplier for other risk factors.

Sedentary Lifestyle

Aerobic exercise and strength training decrease the risk of developing osteoarthritis. The best practice is to follow CDC recommendations: 150 minutes per week of moderate exercise such as brisk walking or 75 minutes of vigorous exercise such as running or cycling. Strength training twice a week.

Smoking

Smoking causes inflammation and double the risk of getting osteoarthritis. It is best to never start smoking. If you smoke, stopping smoking decreases your risk, although not as much as if you never smoked

Avoiding Certain Occupations and Sports

Occupations that involve long standing, bending and heavy lifting increase the risk of osteoarthritis, especially of the knees. They include workers in construction, firefighting, agriculture, fisheries, forestry, and mining. In a case-control study, men who worked for 11–30 years in building and construction work had a 3.7 fold greater risk of developing knee osteoarthritis.

Certain sports such as American football, soccer, competitive wrestling and competitive weight lifting are also associated with increased risk of osteoarthritis of the knee and ankle. There is conflicting evidence about long distance running. Some studies show increased risk, but one study showed that marathon runners have decreased risk of developing osteoarthritis.

How to manage osteoarthritis of the knee

Weight loss

If you are significantly overweight or obese then weight loss will decrease stress on the knee thereby reducing pain and slowing the progression of the arthritis.

Exercise

Aerobic exercise helps pain from knee arthritis. The best exercise is walking or swimming or water aerobics. Strengthening exercises for the quadriceps muscle are also helpful. Here is a link to a good description of quad strengthening exercises: Knee Arthritis Exercises. Physical Therapy can also be helpful and can provide equipment like braces or heel wedges that can also reduce pain. There is also some evidence that tai chi reduces knee pain from knee arthritis. If you smoke, stopping smoking can reduce inflammation and therefore pain.

Medicines

The first medicines to try with the least potential for side effects are topical medicines that you rub on the knee. The most effective ones are diclofenac and capsaicin. Both of these are available over the counter. Topical lidocaine patches can help temporarily, but don’t last as long as the other two.

Oral medicines that are the most effective are NSAIDs like naproxen or ibuprofen in combination with acetominophen (Tylenol). Long term use of oral NSAIDS can occasionally cause bleeding ulcers or kidney damage. If you are taking NSAIDs long term, these need to be monitored by your doctor.

Alternative treatments like glucosamine, ginger and S-adenosylmethionine (SAM-e) seem to help some people and are safe long term. Chondroitin has not been shown to reduce pain.

Joint Injections

Steroid injections in the knee can give temporary relief. This can last for months. These are generally safe every 3 months for up to a year. These injections are easy to administer and can be done by most family physicians without need for referral. Over time, as arthritis worsens they tend to not work as well. Multiple steroid injections have been shown to worsen arthritis, so fewer injections are better.

Cartilage injections have shown no difference from placebo in controlled trials. Some people get some benefit, but this may well be a placebo effect.

Surgery

The only surgery shown to be effective is total or partial knee replacement. Arthroscopic knee surgery to “clean out the joint” has been shown to have no more than placebo effect.

How to manage osteoarthritis of the hip

Exercise

All of the aerobic exercise options for knee osteoarthritis also work for osteoarthritis of the hip, but water exercise or cycling is better than walking. Avoiding certain activities that stress the hip such as stair climbing, or active sports like tennis can reduce pain. Tai chi can also be helpful for hip osteoarthritis. Canes or walkers can be helpful, but need to be prescribed by a physical therapist who can decide on the best appliance and show how to use it properly.

Medicines

Topical medicines do not work as well for osteoarthritis of the hip as well as they do for the knee. Oral medicines are the same as medicines for osteoarthritis of the knee.

Joint Injections

Steroid injections of the hip can be helpful but have to be done using ultrasound or x-ray to make sure the needle is in the hip joint. They are much more difficult than steroid injections of the knee.

Surgery

Hip replacement is the only surgical option. It tends to be less painful post operatively than knee replacement and requires less rehabilitation by physical therapy.

How to manage osteoarthritis of the hands

Home management

Home management includes periodic resting of the hands when doing repetitive activities such as typing. Heat also helps. A warm compress or paraffin wax hand bath can soothe affected joints.

Some adaptations of daily activities may be helpful. Here are some suggestions from Arthritis Health by Veritas:

Wear coats and shirts with zippers instead of buttons
Use long zipper pulls which are also larger than regular zipper pulls and therefore easier to grasp. Specialized zipper pulls are made with looper cloth or nylon and allow the user to stick a finger through and pull down.
Choose lightweight cooking and gardening tools that are easier to lift and hold
Buy slip on shoes to avoid having to tie shoelaces

Occupational therapy can provide hand exercises as well as splints and other home aids.

Medicines

Topical medicines also work well for hand and wrist osteoarthritis. The other medicines for knee osteoarthritis also can be helpful.

Joint Injections

Steroid injections can be very helpful, but are somewhat more difficult to do than knee injections. Hand or wrist steroid injections are usually done by an orthopedist or rheumatologist.

Surgery

Surgery for hand osteoarthritis is not done very often and when done usually involves fusion of a joint to relieve severe pain.

Management of Osteoarthritis of the spine

Osteoarthritis can happen in any part of the spine, but osteoarthritis in the lumbar spine is the most common. The symptoms are back pain, and if a nerve root is compressed, then the pain can radiate down one leg (or one arm if the arthritis is in the cervical spine). Treatment depends somewhat on the symptoms, but like other forms of osteoarthritis non-medication treatment includes exercise, weight loss, tai chi, and physical therapy. Acupuncture helps some people. TENS units sometimes help as well. If you smoke, stopping smoking decreases inflammation and therefore pain.

Medicines

The same topical and oral medicines for knee arthritis also help for spinal osteoarthritis.

Injections

Epidural (just outside the spinal cord sack) injections can be helpful and when they work can last for months or even years. They have to be given by a pain management specialist under x-ray guidance.

Surgery

There are several kinds of spinal surgery. If the spinal osteoarthritis is severe enough to cause pressure on the spinal cord, then part of the vertebrae compressing the spinal cord are removed and the vertebrae are fused. If just the opening between the vertebrae is pressing on a nerve, then that opening is enlarged to take pressure off the nerve root. Surgery can also involve fusion of vertebrae at one or several levels to decrease pain. This kind of fusion surgery is not always successful long term and should be avoided if possible.

Bottom Line

Osteoarthritis is the most common form of arthritis and prevalence increases with age. Over half of people over 75 have osteoarthritis. Women are more commonly affected than men, especially after menopause. Thirty per cent of osteoarthritis is genetic and the rest due to other risk factors including previous joint trauma, obesity, smoking, sedentary lifestyle, certain occupations and certain sports. Avoiding obesity altogether or losing weight if you are overweight, regular aerobic exercise as well as strength training twice a week and stopping smoking if you smoke all decrease your risk of developing osteoarthritis. For those who have osteoarthritis Non-medication treatments should be tried first. Surgery is a last resort when other methods have failed.

Understanding Cancer Screening Tests: Absolute vs Relative Risk Reduction

The benefit of cancer screening tests like pap smears, colonoscopy, mammography and others are reported in two ways. The most common way is the relative risk reduction. This is a ratio of the risk in the screened group divided by the risk in the non-screened group. Relative risk does not take into account the baseline risk in the whole population. The other way of reporting benefit of a screening test is called absolute risk reduction. Absolute risk reduction is the risk in the non screened group minus the risk in the screened group. Relative risk reduction always looks a lot bigger than absolute risk reduction because it does not take into account the baseline risk. Absolute risk reduction is what you really want to know. Absolute risk reduction lets you know how much your risk is reduced by taking the screening test. It is always a lot lower than the relative risk reduction. Absolute risk reduction of the most common cancer screening tests is very low, usually 1% or less.

Here are some examples:

Mammography: Relative breast cancer death risk reduction 30%; Absolute cancer death risk reduction 1%
Colonoscopy: Relative colon cancer death risk reduction 50%; Absolute death risk reduction 0.15%
Pap Smear: Relative cervical cancer death risk reduction 80%; Absolute cervical cancer risk reduction .08%
PSA (test for prostate cancer): Relative risk reduction 64%; Absolute risk reduction .09%

Another number that can be helpful is called Number Needed to Screen (NNS). NNS is the number of people who need to be screened to prevent 1 death from the disease. NNS is just 1 divided by the absolute death risk reduction for the screening test. Here are the NNS’s for the examples above.

Mammography: NNS 1/.01= 100 (this is mammograms every 2 years from age 50-75 so the the 100 patients means about 1100 mammograms).
Colonoscopy: NNS 1/.15=667
Pap Smear: NNS 1/.08=1,440
PSA: NNS 1/.09 =1,111

Sensitivity and Specificity

Any test, including cancer screening tests have a certain sensitivity and specificity.

Sensitivity

The sensitivity of a test is the probability that the test will detect the disease if it is present. In other words it measures how likely it is to get a false negative test. The higher the sensitivity, the less likely the test will be negative if the person has the disease being tested for. It is expressed as a percentage.

Specificity

The specificity of a test is the probability that a person with a positive test will have the disease. In other words it measures how likely it is to get a false positive test. The higher the specificity, the more likely a person with a positive test will have the disease. It is also expressed as a percentage

An ideal test has both a high sensitivity and specificity. Lets look at the sensitivity and specificity of our cancer screening tests.

Mammography: sensitivity 72%; specificity 98%
Colonoscopy: sensitivity 85%; specificity 90%
Pap Smear with HPV testing: sensitivity 95%; specificity 97%
PSA: Sensitivity 30%; Specificity 91%

Bayes Formula

All of these cancer screening tests have high specificity but somewhat less sensitivity except for Pap smears with HPV testing, which have high sensitivity and high specificity. So why are the absolute death reductions so low? Part of it has to do with something called Bayes Formula. It turns out that the chance of a false positive has to do not just with the specificity, but also the frequency of the disease in the population being screened. If the frequency of the disease in the population being screened is low, then even with a test that has high specificity, the chance of a positive test being a false positive is higher than than the specificity would suggest. The frequency of all of the above cancers is low in any 1 year in the population so that means that false positive cancer screening screening tests are common. Below are population frequencies for each cancer per year.

Breast cancer: annual prevalence in women 0.13%. Chance of a positive mammogram being a true positive: 28%. This means that a positive mammogram has 72% chance of being a false positive. On the other hand, a negative mammogram has an 8.7% chance of being a false negative, that is of missing a breast cancer
Colorectal cancer: annual prevalence in population .03%. Chance of a positive colonoscopy being a true positive: 2.5%. That means that a colonoscopy that finds something only has a 2.5% chance of being cancer. On the other hand, a negative colonoscopy has only a .005% chance of being a false negative. That means a negative colonoscopy has only a tiny chance of missing a cancer.
Cervical Cancer: annual prevalence in population 0.0077%. Chance of a positive pap smear being cancer: 0.24%. That means that 99.86% of positive pap smears with HPV testing will not be cervical cancer. On the other hand the chance that a negative pap smear with HPV testing will be a false negative is .00041%. Obviously a negative pap smear with HPV has an infinitesimally small chance of missing a cervical cancer. Although the chance of finding a cervical cancer is very low, the pap smear with HPV also finds precancerous changes in the cervix. Treatment of these precancerous cells prevents cervical cancer from developing. That is a big reason why the prevalence of cervical cancer is so low.
Prostate Cancer: annual prevalence in men .66%. Chance of a positive PSA (>4) being a true positive 2.18%. That means a PSA of >4.0 has a 98% chance that no prostate cancer is present. On the other hand a PSA of <4.0 has a 5.1% chance of missing a prostate cancer.

The somewhat lower sensitivity of mammography, colonoscopy and especially PSA means that false negatives are fairly common, for these tests.

The combination of false positives, false negatives and low prevalence of these cancers in the population all contribute to the small absolute death risk reduction for all four of these cancer screening tests. For patients at substantially higher risk, such as strong family history of breast or colon cancer, the screening tests perform much better, because the high risk population has a much greater disease prevalence than the general population.

Over Diagnosis

Another problem with cancer screening tests is over diagnosis. Over diagnosis means that a positive test finds a cancer, but the cancer grows so slowly or spontaneously disappears so that it never would have caused any symptoms in the person. Over diagnosis then leads to unnecessary treatment. So let’s look at the over diagnosis rate for our four cancer screening tests.

Mammography: Over diagnosis rate for women 40 and over is 12%. This means the 12% of women diagnosed with breast cancer by mammography will be treated for cancer unnecessarily.
Colonoscopy: The over diagnosis problem with colonoscopy results from the removal of polyps. All visible polyps are removed during colonoscopy. The polyps that have some chance of turning into cancer are called adenomatous polyps. Only 8% of these turn into invasive colon cancer over 10 years. That suggests that 92% of the adenomatous polyps removed at colonoscopy would never turn into cancer. Removal of all adenomatous polyps does prevent some colon cancers. It is not possible to know at the time of removal which polyps are going to progress. The cost of prevention of some colorectal cancers is substantial over diagnosis.
Pap Smear with HPV: Overdiagnosis of precancerous cervical lesions is high. We now know that cervical cancer is caused almost exclusively by the HPV virus. On the other hand, women often clear an HPV infection on their own without treatment. This is particularly the case with young women, which is why pap smears and HPV testing are not recommended before age 21. Precancerous cervical lesions are graded CIN1-CIN3, CIN3 being the most severe. Overdiagnosis rates are higher for the lower grade lesions, which most often clear on their own. The figures for over diagnosis over women’s lifetime were 70.6% for CIN1+, 63.2% for CIN2+, and 50.0% CIN3+.
PSA test for prostate cancer: Low grade prostate cancer is common as men age. Many of these cancers would never cause symptoms during the lifetime of the men. Current estimates are that 60% of prostate cancers detected by PSA would never cause symptoms or death from prostate cancer. Treatment of prostate cancer often results in permanent urinary incontinence and/or sexual dysfunction. This very large over diagnosis and therefore unnecessary treatment is why PSA testing is so controversial. There are certain populations of men who are at high risk of aggresive prostate cancer and these men are probably the only ones who should have routine PSA testing. Here is a link to a risk calculator for prostate cancer: PCPT Risk Calculator.

Bottom Line

Despite the high specificity of cancer screening tests, Bayes Formula shows that false positive tests will be more frequent than true positive tests. For mammograms, colonoscopy and PSA the somewhat low sensitivity means that there will be some false negative tests. In other words, they will miss a few cancers. Pap smear with HPV has the lowest chance of missing a cancer. Over diagnosis is a problem with all cancer screening tests, resulting in unnecessary treatment. This is particularly a problem for breast cancer and especially prostate cancer. The low absolute death risk reduction values and the over diagnosis problems for these tests do not mean you should not be screened, especially if you are in a higher risk population due to family history or other causes of higher cancer risk. All of these screening tests save lives, just not as many as the relative risk values suggest. The vast majority of people will not benefit from these tests and some will be harmed by unnecessary treatment, but a small but substantial number will have their lives saved.