Asymptomatic COVID-19 carriers may have viral loads on par with patients with symptoms, though a slightly higher proportion of symptom-free individuals may test negative within a few weeks of diagnosis, according to a new study.
"Because transmission by asymptomatic patients with SARS-CoV-2 may be a key factor in community spread, population-based surveillance and isolation of asymptomatic patients may be required," co-first and corresponding author Eunjung Lee, an internal medicine researcher at Soonchunhyang University in South Korea, and colleagues wrote in a paper published in JAMA Internal Medicine on Thursday.
Using RT-PCR, the researchers assessed samples from 303 COVID-infected individuals between the ages of 22 and 36 years old who were treated at a community treatment center in the Korean city of Cheonan — a group that included 110 individuals who were symptom-free when they went into isolation.
A subset of just over 19% of the initially asymptomatic patients did eventually experience COVID-19 symptoms, typically within between 13 and 20 days of being isolated. But the remaining asymptomatic individuals remained free of notable symptoms over a follow-up time of between 20 and 26 days.
The team noted that viral load appeared to be comparable in the asymptomatic and symptomatic cases, based on RT-PCR cycle threshold, or Ct, values. Such results hint that symptom-free individuals may be transmitting disease, though the study did not directly test that assumption.
"In this cohort study of symptomatic and asymptomatic patients with SARS-CoV-2 infection who were isolated in a community treatment center in Cheonan, [Republic of Korea], the Ct values in asymptomatic patients were similar to those in symptomatic patients," the authors reported, calling the viral shedding in both groups "prolonged."
Notably, the study also offered a look at the proportion of patients who went on to test negative for SARS-CoV-2 over time. After two weeks, nearly 34% of the asymptomatic patients became SARS-CoV-2-negative based on RT-PCR testing — the proportion of negative cases grew to just over 75% in the symptom-free cases tested again at the day 21 post-diagnosis timepoint.
In the symptomatic COVID-19 group, the number of negative tests dipped somewhat compared to the asymptomatic groups, with 29.6% showing negative test conversion after 14 days and just shy of 70% testing negative within 21 days of diagnosis.
The authors noted that "it is possible that the asymptomatic patients in our cohort were not representative of all asymptomatic patients in the community because false negatives would not have been included in our sample," and further cautioned that "we did not determine the role that molecular viral shedding played in asymptomatic patients."