Viral shedding from asymptomatic COVID-19 patients may be prolonged

Not only do asymptomatic COVID-19 carriers have viral loads that are similar to symptomatic patients, they could remain asymptomatic for a prolonged period of median 24 days from diagnosis, reveals a study.

Hence, viral shedding could also be prolonged in asymptomatic people — sparking concerns on potential transmissibility of asymptomatic infections.

Among 303 patients (median age 25 years, 66.3 percent women) who tested positive for SARS-CoV-2 by RT-PCR, about one-third (36.3 percent) were asymptomatic at diagnosis. [JAMA Intern Med 2020;doi:10.1001/jamainternmed.2020.3862]

Of note, 84.6 percent of the asymptomatic patients remained so for a median of 24 days from diagnosis.

Despite being asymptomatic, these patients carried similar viral loads as those who were symptomatic, as indicated by Ct values of RT-PCR test. 

However,  viral loads of asymptomatic patients tended to decline more slowly than symptomatic patients, with respect to the envelope (env) gene of SARS-CoV-2 detected from lower respiratory tract specimens (β=−0.065; p=0.005 for time interaction).

Meanwhile, the drop in other genetic segments encoding for viral nucleocapsid protein and RNA-dependent RNA polymerase were not significantly different between asymptomatic and symptomatic patients.

The median time to negative conversion among asymptomatic patients was 17 days compared with 19.5 days in symptomatic patients (p=0.07). At 14 days, 33.7 percent and 29.6 percent of asymptomatic and symptomatic patients, respectively, showed negative conversion at day 14. The corresponding negative conversion rates at day 21 were 75.2 percent and 69.9 percent, respectively.

“It is important to note that detection of viral RNA does not equate infectious virus being present and transmissible,” cautioned the researchers.

Even so, the results do not support the notion that infected individuals without symptoms are less likely to spread or be cleared of the virus sooner than symptomatic patients.

“An important implication of our findings is that there may be substantial under-reporting of infected patients using the current symptom-based surveillance and screening,” the researchers highlighted.

“Many individuals with SARS-CoV-2 infection remained asymptomatic for a prolonged period ... [and thus,] viral molecular shedding was prolonged,” they noted. “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.”

As the study cohort involved young, healthy patients, the researchers said the findings should not be generalized to the whole population at large. Another limitation was that the role of molecular viral shedding in transmission from asymptomatic patients is also unknown.