After my last grim post, one of my friends suggested that I should post pictures of a baby bunny and a puppy to ameliorate the unpleasant conclusion. This post will be more upbeat, I promise.
Testing
PCR Tests
There are two kinds of tests. One kind tests for the presence of the virus itself from nasal secretions or saliva. The method used to detect the virus is called PCR (polymerase chain reaction). This is the same method used to detect the influenza virus during flu season. This method amplifies ( makes millions of copies of) a small piece of the RNA from the virus. There are several ways to “tag” the RNA so that it can be measured. This is a very sensitive and specific test. There are few false negatives, and almost no false positives.
Antibody Tests
The other kind are antibody tests. These tests measure antibodies that infected people make in response to the virus. Antibodies do not develop until about 3 weeks after infections with SARS-COV-2. There are many of these tests on the market now and most of them perform poorly. There are lots of false positives and false negatives. There are only four of these antibody tests that have been approved by the FDA. At some point fairly soon we will figure out which are the best antibody tests, but right now it is like the wild west. Antibody tests may be useful for states and municipalities in order to figure out how widely SARS-COV-2 has spread in a specific population. At this point we do not know for sure if testing positive for antibodies means that you are immune to re-infection with SARS-COV-2. There is no reason now for an individual to purchase or try to get one to these tests. I will not talk about antibody tests any more in this post. Further discussion will be for a later post when more information is available about the best tests and how they are being used.
How many tests are needed?
There has been a lot of reporting in the news media lately about how many tests (PCR tests) are needed in order to contain the epidemic. Estimates for the number of tests needed range widely, creating a lot of confusion. Gradually opening the economy successfully means that we have to be able to recognize and contain new outbreaks. New outbreaks will inevitably occur as we begin to decrease social distancing no matter how carefully we do it. Recognizing outbreaks requires robust testing as well as contact tracing and isolation of cases and contacts. More about contact tracing later.
How much testing do we need to recognize outbreaks? The answer is, it depends. First of all, states and localities that are seeing increasing numbers of new cases and hospitalizations need to maintain stay at home orders. Testing and contact tracing should be only be used for those states and localities that are showing decreasing numbers of cases and hospitalizations.
The best measure of whether enough tests are being done is the percent of positive tests of all tests being done. If the positive test percentage is 10% or less, that means that enough testing is being done to identify new outbreaks. The number of tests needed for states and localities that have only a few cases and deaths is much smaller than the number of tests needed for states with lots of cases and deaths. For example Montana, which has few cases and deaths would need to do between 31 and 156 tests per day to meet the 10% positive standard. New York, on the other hand, which has huge numbers of cases and deaths would need to do 130,000 to 155,000 tests every day to meet the 10% positive standard. About half the states will have to increase their current level of testing significantly to meet the 10% positive standard. Here is a link to the STAT-news website, which has a map showing testing gaps by state. A negative number means the state will have to increase testing by that much per day. A positive number means the state is already doing enough tests. In the last week, the U.S. as a whole conducted 1.6 million tests, according to the Covid Tracking Project. The Harvard team says twice that many tests will be needed — at minimum.
What has not been made clear to the public is that adequate testing volume varies hugely by state and even counties within states. The good news is that half the states have the capacity to do adequate testing. The states that need very large numbers of tests per day are unlikely to manage this on their own. They will need help from the federal government.
Contact Tracing
Contact tracing is done by identifying cases (through testing) and then calling or visiting all the people who have had direct contact with the case. The contacts are asked to isolate for a period of time equal to the longest incubation period of the disease in question. For COVID-19 that is about 2 weeks. The case is isolated until he/she no longer tests positive (anywhere from three to five weeks for COVID-19). Successful contact tracing limits the spread of outbreaks and helps stop transmission of infections. Health departments have been doing this for years with infectious diseases such as sexually transmitted diseases, measles and tuberculosis, among others. These outbreaks are usually small enough to be manageable by the normal staff of health departments.
Contact tracing for COVID-19 is an order of magnitude bigger job and will require thousands of contact tracers. Estimates range from 100,000 to 300,000 for the entire country. Recruiting and training that many contact tracers is going to be a huge task. Some states, notably Massachusetts and California are already recruiting and training contact tracers.
Technology could help with contact tracing. Apple and Google are collaborating on a system that uses Bluetooth to identify when your smart phone (either iphone or android) is within 6 feet of another smartphone. In order to protect privacy, the location of anyone’s phone is not recorded. The system works like this. Go to this link to see the Wired magazine article describing this. Each phone will broadcast constantly changing Bluetooth codes . If phones get within 6 feet of one another for a certain period of time (say 10 minutes), each phone will record the number and save it. When a user reports a positive Covid-19 diagnosis, their app notifies everyone that was within 6 feet of that person in the last two weeks and will let them know that they may have been exposed, and will then show them information about self-quarantining or getting tested themselves.
To prevent people from “spoofing” the system and reporting that they have COVID-19 when they do not, a special code would be required to activate the contact network notification. That code would only be provided by clinicians who report positive test result to patients.
Success using this technology will depend on how many people are willing to use it. Also, it requires smartphones. Since COVID-19 cases disproportionately affect economically disadvantaged people, many of them do not possess smartphones. Although this technology may help, it will not significantly decrease the number of people needed to do contact tracing.
Bottom Line
Re-opening the economy will lead to new outbreaks. In order to contain and limit those outbreaks robust testing and contact tracing will be required. States need enough testing capacity so that 10% or less of tests are positive. That amount of testing will vary depending on how many cases a state or locality has. Massive numbers of people will be needed to be trained to do contact tracing. Technology can help, but has limitations.