A review of dozens of studies by researchers at Oregon Health & Science University and Oregon State University suggests that people may shed virus for prolonged periods, but those with mild or no symptoms may be infectious for no more than about 10 days. People who are severely ill from COVID-19 may be infectious for as long as 20 days.

That's in line with guidance provided by the US Centers for Disease Control and Prevention, confirming recommendations for the length of time people should isolate following infection with SARS-CoV-2.

The review published in the journal Infection Control and Hospital Epidemiology.

"Detection of viral RNA may not correlate with infectivity since available viral culture data suggests shorter durations of shedding of viable virus," the authors write. "Additional data is needed to determine the duration of shedding of viable virus and the implications for risk of transmission."

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Researchers decided to conduct the review to gain more information on transmission and to help inform infection control practices, said co-author Monica Sikka, MD, assistant professor of medicine (infectious diseases) in the OHSU School of Medicine.

"Even though people can shed virus for a prolonged period of time, the studies we reviewed indicated that live virus, which may predict infectiousness, was only detected up to nine days in people who had mild symptoms," Sikka said.

The researchers identified 77 studies worldwide, including 59 that had been peer-reviewed, and combed through the results. All studies reported assessments of viral shedding using standard methods to identify the virus by replicating it through a process called polymerase chain reaction, or PCR.

"Although PCR positivity can be prolonged, culture data suggests that virus viability is typically shorter in duration," the authors write.

- This press release was originally published on the OHSU News website