Aug. 6 (UPI) -- People with confirmed COVID-19 who don't have symptoms of the disease are as contagious as those with symptoms and may need to be isolated to prevent spread of the virus, according to a study published Thursday by JAMA Internal Medicine.
Asymptomatic COVID-19 patients included in the analysis continued to test positive for the virus for up to 18 days after diagnosis, slightly less than the 20 days for those with symptoms, the researchers said.
Viral loads -- the amount of virus in an infected person -- in samples collected from the lower respiratory tract of patients also declined more slowly in those without symptoms than in those with them, they said.
Many asymptomatic patients also had evidence of "viral shedding" -- meaning they were contagious -- for at least 30 days after confirmed diagnosis, according to the researchers.
"Little is known about the infectiveness of asymptomatic patients," South Korean researchers wrote in the study. "Our findings ... nevertheless offer biological plausibility ... of transmission by asymptomatic people."
The findings were based on an analysis of 303 patients with confirmed COVID-19, 81% of whom didn't have symptoms at the time of diagnosis.
Patients included in the study ranged in age from 22 to 36, and 110 -- or roughly 36% -- were asymptomatic at the start of the analysis, the researchers said.
All of the patients were isolated in the COVID-19 ward of a South Korean hospital, and 21 -- about 19% -- of the asymptomatic patients developed symptoms while in isolation.
Seventy-five percent of the asymptomatic patients tested negative for the virus -- an indication of recovery -- 21 days after diagnosis, compared to just under 70% of symptomatic patients, the researchers said.
"Viral molecular shedding was prolonged," the researchers wrote. "Because transmission by asymptomatic patients with [COVID-19] may be a key factor in community spread, population-based surveillance and isolation of asymptomatic patients may be required."