MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.
An individual working in the same lab as me has tested positive for COVID-19 and is self-isolating at home with mild symptoms. My understanding of MIT’s rules is that this person cannot get tested again at MIT for 90 days, but they are cleared to come back in the lab after 10 days.
My lab mates and I are concerned about MIT’s policy of allowing people to come back to campus without first getting a negative test. This makes us feel unsafe and may risk spreading the virus. We’re wondering if MIT would consider changing its policy or might selectively retest people who will be going back to work with others in labs or offices?
First of all, it’s important to note that these are not MIT’s rules; rather, MIT is following guidance from the CDC, which is identical to recommendations from the Massachusetts Department of Public Health and is firmly rooted in science.
Based on these guidelines, individuals with mild to moderate cases of COVID-19 must self-isolate for 10 days from symptom onset or until they are fever free for at least 24 hours (without the aid of fever-reducing medications), whichever is longer. Asymptomatic individuals who test positive must self-isolate for 10 days from the date of the positive test.
Why 10 days? Because researchers at the CDC and elsewhere have failed to successfully culture replication-competent virus obtained from individuals more than nine days after symptom onset. According to the CDC’s Symptom-Based Strategy to Discontinue Isolation for Persons with COVID-19 Decision Memo [PDF], “the statistically estimated likelihood of recovering replication-competent virus approaches zero by 10 days.”
Individuals who are not shedding replication-competent virus are not infectious and cannot transmit the virus to others.
So, why not retest? Because, while these individuals cannot spread the virus to other people, they may continue to shed non-infectious viral RNA that the PCR test will detect, returning a positive result. Although the person’s immune system has neutralized the virus, preventing it from continuing to replicate, nucleic acid from the virus remains and degrades slowly over time.
To be clear, this shedding of non-infectious viral particles is not unique to SARS-CoV-2. It’s a phenomenon we can observe with many viruses, including SARS-CoV, MERS, influenza, Ebola, Zika, and measles. These viral remnants are not infectious — they are the equivalent of a few hairs left on the pillow after someone has gotten out of bed. But the PCR test for COVID-19 cannot distinguish between whole virus capable of infecting other people and the non-infectious viral debris that people continue to shed after an infection.
For this reason, public health guidelines specify that an individual’s return to their usual activities after a period of self-isolation should not be contingent on a negative test result.
Once they have completed the prescribed period of self-isolation, individuals who have tested positive for the virus or have recovered from COVID-19 are unconditionally cleared to return to their labs, classrooms, or offices on campus. People who have been ill with COVID-19 may continue to have some symptoms — cough, fatigue, continued loss of smell or taste, even some shortness of breath — for several weeks after recovery. But they are not infectious, and they should not be feared, shunned, or subject to retesting or additional scrutiny.
Stigma related to COVID-19 has led to discrimination, even violence, against healthcare workers, Asian Americans, and individuals who have recovered from the illness. Some people have been fired from their jobs after testing positive. Anxiety about this new virus is understandable, but, as the CDC also reminds us, our actions should be dictated by facts, not fear. And nowhere should this be this truer than at MIT, where we are committed to following both public health guidance and the science.