The accuracy of tests for SARS-CoV-2 is central to our ability to control the epidemic— knowing who is infected, who has been exposed, and who is immune. It is also central to our ability to reopen businesses and lift restrictive lockdown measures. Unfortunately, our tests are not up to the job, nor are they available and affordable to all those in need. But that does not mean we don’t have ways to blunt the damage that our testing failures may cause.
As Bloomberg reported over the weekend, doctors trying to diagnose patients are saying that false negative results from coronavirus tests are becoming an increasing concern, impeding their ability to correctly diagnose patients and preventing us from truly understanding the spread of the disease. The tests for the presence of the virus itself can miss thirty to forty percent of those actually infected, sometimes even more. These false negatives are due in many cases to individual variation in the actual level of the virus, the technique used by the tester, and issues with the tests themselves.
The antibody tests that detect prior infection also have issues. As the FDA package insert warns, these tests are not specific for SARS-CoV-2. They also detect prior infection by coronaviruses that are not related to COVID-19, instead noting antibodies developed in response to milder coronaviruses that circulate among us causing symptoms more like the common cold. Also troubling is the observation from China that up to one third of convalescent patients—meaning those hospitalized but not placed in ICU isolation—do not have detectable antibodies, even though they are symptom free. There is also emerging evidence of virus reactivation or reinfection in convalescent populations.
The consequences are that some asymptotic carriers will be missed and continue to spread the infection. Others who think they are immune will remain at risk for reinfection and some may continue to transmit the virus to others unknowingly.
The challenges with testing for COVID-19 infection are important to consider as cities and states plan strategies to reopen businesses and return to more of a sense of normal. Without more accurate tests, we must ensure repeated testing of those identified as having been exposed for traces of SARS-CoV-2 and continued long term follow-up screening of all convalescents for the presence of the virus. Erring on the side of caution and testing more often than some may deem necessary is imperative in order to mitigate the very real risk of a new outbreak emerging just as we begin to get the current outbreak under control.