TESTING THE LIMITS OF MASS TESTING

IT is understandable why people would place a lot of hope on mass testing, whatever it means. For many, the peace of mind from knowing whether one or someone you love is negative for the coronavirus would mean a lot in the face of uncertainty.

We already heard about the Alliance of Concerned Teachers’ (ACT) demand that there should be no opening of classes without mass testing of both teachers and students. Marikina City has launched a mass testing of all its tricycle drivers. Workers are demanding from employers that there should be mass testing as a prerequisite for them to return to work, and employers are asking for government assistance; only to be told by Malacañang that they have to shoulder the cost themselves.

Palace spokesman Harry Roque became the object of much criticism not only when he redirected the burden for mass testing of workers toward employers, but also when he claimed that there is no country in the world that has conducted mass testing of all its citizens. Roque is being faulted for equating mass testing to mean that every single person would be tested. Memes erupted in the internet ridiculing Roque for misconstruing what mass testing means, pointing out that mass weddings don’t mean everyone is wed or mass burial that everyone is buried.

Yet, if you look at the manner in which the term is ordinarily used, what is in fact actually meant by ACT is to test all teachers and students, and by workers for all of those working in a particular company to be tested. After all, when Ateneo mass promoted its students, it literally promoted all of them. And when the vaccine will be available, there will be a move to mass vaccinate everyone.

This is where the discourse on mass testing becomes problematic and muddled. The concept becomes a political battlecry of citizens hoping that it will help in protecting them from the virus and is seen as a panacea, as if when one is swabbed for samples or blood is drawn from them and the result is negative, that one is safe. There are also those who think that testing as many people as possible will give us an accurate picture of the extent of the prevalence of the coronavirus disease of 2019 (Covid-19) vis-à-vis the entire population.

The thing is, it is not as easy as that. There are actually two kinds of tests. If you want to know the prevalence of Covid-19, then there is a need to conduct epidemiological testing. This requires testing a statistical sample of between 4,000 to 5,000 randomly selected individuals. This would be useful for policy decision making since it will give us a view of the extent in terms of the location and number of infected persons. However, it would not useful to venture into testing a targeted vulnerable sector, like those with co-morbidities and who are likely exposed since it may produce results that can over-estimate the prevalence of the disease.

On the other hand, if the purpose is to ascertain if a person is infected, what is done is clinical testing. This will generate an assessment of whether the person is infected or not. On a larger scale, it is this kind of testing that is expanded to target types of people, particularly those who have history of exposure, or are showing symptoms, or have co-morbidities or are at risk such as frontliners. Here, the purpose is to clinically assess the presence of the virus in these people so that proper measures such as quarantine, treatment and contact tracing can be done. This kind of testing, however, cannot be used to measure prevalence relative to the entire population.

The problem with testing, however, is that while it is effective in confirming infection of persons who are already showing symptoms, it may not be as effective for asymptomatic persons, whether infected or not.

Rapid testing kits and even the more reliable enzyme-linked immunoassay, or Elisa, test for the presence of antibodies are therefore is of no use for asymptomatic people, infected or otherwise. Antibodies only present themselves in infected people and in order for it to reveal a positive test, they should be at a substantially large number. This happens when the person already shows symptoms. In fact, according to University of the Philippines epidemiologist Dr. Edsel Maurice Salvana, antibody tests yield positive results only seven days after the onset of symptoms and are best done two weeks after considering that antibodies only become prevalent when the patient is on the way to recovery.

Real-time reverse transcription polymerase chain reaction (RT-PCR), on the other hand, tests for the genetic material of the virus. But, again, this test is best done when the person has already shown symptoms. Dr. Salvana warns that doing the test too early or too late may not detect the virus and may yield false negatives.

Thus, if you do either the antibody or the RT-PCR tests on healthy or even infected but asymptomatic persons, like teachers, students, workers and tricycle drivers, it cannot give you a helpful outcome since it is likely to yield negative or false results. These tests become more reliable when the person is already showing symptoms and you want to know if it is Covid-19 or something else. However, when a person is already symptomatic, then there is no more need to test if the only intention is to screen people for purposes of work or school. The person is already showing physical symptoms which can then be used as basis for the appropriate course of action by the school or employer.

Now, what is even scary is that even if your antibody test turns out to be positive, it may not even be because of Covid-19, but of other coronaviruses such as the common cold. Experts note that two out of three rapid antibody tests results end up as false positives.