Patients With Mild, Moderate COVID-19 Unlikely to Be Infectious After Day 10 of Symptom Onset

October 14, 2020

By Denise Baez

NEW YORK -- October 13, 2020 -- Patients with mild to moderate coronavirus disease 2019 (COVID-19) are highly unlikely to be infectious after day 10 of symptom onset, however, patients with severe disease may shed the virus for a longer period of time, according to a study published in the Journal of Infection.

The findings come from a rapid review of 13 virus culture studies and 2 contact tracing studies conducted between January 1, 2020, and August 26, 2020. The studies were conducted in the United States, the United Kingdom, Taiwan, Germany, Switzerland, Australia, Canada, Spain, South Korea, Hong Kong, and the Netherlands.

Across all 13 virus culture studies, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) culture was attempted from samples collected from at least 808 patients, with SARS-CoV-2 isolated in at least 206. A total of at least 1,652 samples had SARS-CoV-2 culture attempted and at least 413 of these were positive.

For 5 of the virus culture studies, the last day on which SARS-CoV-2 could be cultured occurred within the first 10 days since onset of symptoms. For the most part, the clinical severity of patients was mild to moderate in these 5 studies. For another 5 virus culture studies, SARS-CoV-2 was isolated beyond day 10 for approximately 3% of included patients. The remaining 3 virus culture studies included patients with severe or critical disease. In one of these studies, SARS-CoV-2 was isolated up to day 32, and in 2 studies that included immunocompromised patients, SARS-CoV-2 was isolated for up to 20 days.

The 2 large contact tracing studies reported that when close contacts were first exposed greater than 5 days after symptom onset in the index case, there was no evidence of laboratory-confirmed onward transmission of SARS-CoV-2.

“The evidence to date from virus culture studies would appear to suggest that patients with mild-to-moderate COVID-19 are highly unlikely to be infectious beyond 10 days from symptom onset,” wrote Kieran A. Walsh, MD, Health Information and Quality Authority, Cork, Ireland, and colleagues. “Evidence from large contact tracing studies appears to support this finding. However, evidence from a limited number of studies indicates that patients with severe or critical illness, and or those who are immunocompromised, may be infectious for a prolonged period, possibly for 20 days or more.”

There were 6 studies that examined the relationship between viral load and culture of SARS-CoV-2, and all 6 studies found an inverse correlation. One study that included 234 samples (Basile et al) concluded that any clinical sample with a cycle threshold (Ct) value of ≥37 was not indicative of replicative (or potentially transmissible) virus. Another study that included 90 samples (Bullard et al) estimated that for every 1 unit increase in Ct value, the odds of culturing SARS-CoV-2 decreased by 32%.

“The findings from our rapid review are largely in agreement with 4 previous reviews conducted in this general area,” the authors wrote. “All of these reviews concluded that infectiousness generally declines 7 to 10 days after symptom onset, and point to uncommon outlier cases where this duration is exceeded. Another common finding across 3 of these reviews was the prolonged duration of SARS-CoV-2 RNA detection, sometimes for 2-3 months after onset of symptoms, along with cases of repeat SARS-CoV-2 RNA detection after a patient has clinically recovered. Hence, patients are unlikely to be infectious for the entire duration of viral RNA detection as the presence of viral RNA may not represent transmissible or replication-competent virus. Our rapid review is the first to attempt to quantify the proportion of patients with COVID-19 that are potentially infectious beyond day 10 post symptom onset, and draws on more recent evidence, including both virus culture and contacting tracing studies.”

Reference: https://www.journalofinfection.com/article/S0163-4453(20)30651-4/fulltext

SOURCE: Journal of Infection