COVID-19 Retesting Should Be Pushed Back to 4 Weeks to Give Virus Ample Time to Shed

How long does it take a person infected with SARS-CoV-2 to finish shedding the virus? Coming up with the answer to this question to make scientifically sound decisions about not only the clinical treatment of the infected but also containment of asymptomatic or minimally symptomatic. Recently published research from Italy shines new light on the duration of virus shedding and need for retesting.

Bottom Line on Top

National regional testing protocols in Italy recommend COVID-19 retesting after 14 days of diagnosis. The study found that testing this early is more likely to result in false negatives and concluded that postponing COVID-19 retesting for 30 days from the date of diagnosis and 36 days from the date of symptom onset increases the efficiency of testing protocols.

The Study

The study was conducted in the Reggio Emilia province of Italy, one of the country’s hottest COVID-19 hotspots. Scientists from the Istituto di Ricovero e Cura a Carattere Scientifico tracked 4,538 patients from the province who were diagnosed with COVID-19 between Feb. 26 and April 22. The study found a higher rate of false negatives for nasal swab tests when they were performed too early in a patient’s recovery.

Of the 4,480 patients included in the researchers’ preliminary analysis, 1,259 achieved viral clearance as indicated by at least one negative swab test following the initial positive test result, with a median time to viral clearance of 31 days. Sadly, 428 patients among this group died. The investigators then performed follow-up testing on 1,162 people who had been diagnosed at least 30 days prior and for whom the date of symptom onset was available. Patients were tested an average of three additional times, with the mean times of retesting about 15 days after the first positive test, 14 days after a second positive test, and nine days after a third positive test.

Viral clearance was detected in 704—nearly 61 percent—of the 1,162 patients and confirmed in roughly 79 percent of those who underwent a second test, suggesting that there was about one false negative for every five negative test results. Median time to viral clearance was 30 days from the first positive swab and 36 days from symptom onset, with the time increasing based on age and disease severity.

However, the rate of false negatives declined when the first negative test was performed more than 34 days after the first positive test.

Retesting Recommendations

The study suggests that it takes four weeks to finish shedding the SARS-CoV-2 and concludes that performing testing 14 days from diagnosis is too early and should be pushed back to more than four weeks.

The investigators also recommend that COVID-19 patients self-isolate for more than 30 days after their symptoms begin or until at least one follow-up test is performed to confirm viral clearance to avoid generating secondary cases.

Takeaway

The study suggests that COVID-19 retesting of infected patients after two weeks is too early and dangerous to the extent it results in releasing false negatives into society before they have shed the virus. Waiting four weeks will not only improve test accuracy but also prevent people who are not fully recovered from infecting others.