In Boston, we are among the earliest proponents of school screenings for COVID-19 as infectious disease specialists and epidemiologists at the forefront of pandemic response. Since we wrote to Massachusetts Gov. Charlie Baker in favor of implementing such an approach, the nearly year-long period has resulted in the state having better access to COVID-19 testing, has provided a better understanding of the disease, and has drastically altered the pandemic landscape. Vaccinating adults also protects children in other countries.
The Reason For Not Blindly Screening Students For COVID-19 In Fall 2018
Schools must rethink their testing policies as the pandemic evolves. Schools where there is little probability of in-school transmission, should not conduct screening.
Different types of testing require critical distinctions. Diagnoses confirm or rule out the presence of an infection in a person with symptoms based on testing for asymptomatic cases of the disease. Screening tests detect asymptomatic cases of the disease.
A short turnaround time for results remains one of the most important elements of free, easily accessible diagnostic testing, and it should be included in the policy, planning, and contracts for the upcoming school year. As an alternative, screening tests – if used at all – should be limited.
A pooled testing program for students and staff is being set up by the Massachusetts Department of Elementary and Secondary Education (DESE) for the 2020-2021 school year to screen for asymptomatic infections. It identified COVID-19 cases among school-aged children as very low – only 0.76% of test pools identified positive results, which translates to a much lower percentage of infected students.
Students in schools are also extremely rare carriers of COVID-19. Several schools remained open thanks to this data, which gave parents and staff a sense of security. As we begin planning the screening tests for next year, we should celebrate and use the results of this program as input.
After all, the screening testing program has been successful, so why do we suggest retirement? This is termed the positive predictive value by epidemiologists. Tests aren’t perfect, plain and simple. In some cases, a test is positive, while the person is not sick (false positives), while in others, the test is negative even if the person is sick (false negatives). Oftentimes, positive test results are false positives in case rates that are low.
Typically, in our minds, clinical tests and test results are black and white – the presence of a disease or its absence. Interpreting test results in real life is difficult, unfortunately. An accurate test depends both on its sensitivity (ability to identify disease cases) and its specificity (ability to identify healthy people as healthy correctly). However, a test’s real-world value is directly linked to the likelihood that a disease will actually occur (population-based disease prevalence). In schools, screening tests are a failing grade.
Even before widespread vaccination, the DESE testing program and others across the state and country showed that the probability of students having COVID-19 in the physical classroom was consistently less than 0.5%. If 0.5 is used as a (very) generous overestimate and a diagnostic test that is very specific (99%), this means for every true positive test; there will be three false positives. Most polymerase chain reaction (PCR) tests have higher specificities than 95% (i.e., pretty good, but not quite as tight as perfect).
Adding this more realistic estimate to that previously mentioned significantly increases the number of false-positive test results. The screening program identifies up to 14 false positives for every COVID-19 case that actually occurs. In the context of declining case rates, the ratio of actual cases to false positives is continuously increasing (and increasing). Assuming that a screening program will find the actual case more often than a false-positive result, there are 14 failed tests for every real case and 71 if we assume a 95% sensitivity.
It is a major theorem of public health (even doctors are known to misapply these principles). There is no mammography performed on teenagers since the prevalence of the disease is so low in this group; screening would lead to a greater number of false-positive cases than true positive cases being appropriately treated. In schools, screening tests are also conducted.
Moreover, because COVID-19 vaccines protect against asymptomatic disease so well, excluding vaccinated individuals from any screening program is essential as recommended by the Centers for Disease Control and Prevention, considering the very reasons we argue it is time to retire the program for everyone.
When the positive predictive value for COVID-19 is low, what are the downsides? False-positive testing has two major effects. First, it keeps students and employees out of school unnecessarily – both the falsely labeled person and any close companions. A good example of the downsides of school screening programs is seen already in the Summer Rising Program in New York City, where many classrooms have been closed after just a few days.
A false-positive result in COVID-19 may also lead to unnecessary therapies and the inadvertent grouping of infected and uninfected people. These programs are costly both financially and in human resources, as well. The benefits seem to outweigh those costs.
What should be done with the testing funds? A diagnostic testing program is preferred over a screening program. As pandemic precautions continue to be rolled back, we expect to see a surge in influenza diagnostic testing this fall and winter, as well as a focus on COVID-19.
The fall semester should see schools looking mostly normal without masks or distancing. We will therefore need to find out as quickly as possible if the child has COVID-19.
In the event that a case is identified, the extensive testing infrastructure piloted this past spring in Massachusetts could prove useful. A quarantine and classroom closure alternative approach could include frequent (daily) screening tests for exposure of adults, allowing exposed children to stay at school, provided no transmission is detected.
The screening program might find additional cases, resulting in the need for quarantine to contain a cluster. The aim of this strategy is to strike a balance between the needs of safety and keeping the children in their classrooms, where they belong.
As epidemiology and science of the pandemic change, we need to be nimble and change tactics. It might be warranted, if cases re-emerge, to implement a screening program to detect unvaccinated staff and students. This would be crucial where students can’t be disengaged from school. A program that keeps healthy children at home hurts more than it helps when it aims to maximize the amount of time our children spend in school.
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