Asymptomatic people who test positive for COVID-19 appear to be just as infectious as people with symptoms — and for a similar, extended time period, according to researchers from South Korea. Isolation is necessary to contain potential transmission, they say.

In a new retrospective analysis, the investigators studied data from 303 younger adult participants (oldest age 36) who were isolated in a community treatment center. The amount of viral load — or the number of infectious virus particles carried — was studied to determine each person’s risk of spreading disease. 

Researchers found similar viral load in symptomatic and asymptomatic adults. What’s more, 81% of initially asymptomatic patients with a SARS-CoV-2 infection remained asymptomatic from 20 to 26 days beyond their diagnosis.

Despite the existence of some early studies and anecdotal evidence, little is known about the infectiousness of asymptomatic COVID-19 patients, first author Seungjae Lee, M.D., of Soonchunhyang University College of Medicine, reported. Based on the study’s results and what is known thus far, “isolation of infected persons should be performed regardless of symptoms,” Lee and colleagues concluded.

The Centers for Medicare & Medicaid Services is promoting a weekly testing regimen in long-term care facilities to catch all potential carries among staff and residents with the goal of treating and containing the virus.

Full findings were published in JAMA Network.