WEDNESDAY, Sept. 23, 2020 (HealthDay News) — Most people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) do not remain asymptomatic, and the secondary attack rate is lower among contacts of people with asymptomatic infection, according to a review published online Sept. 22 in PLOS Medicine.

Diana Buitrago-Garcia, from the University of Bern in Switzerland, and colleagues conducted a systematic review and meta-analysis to examine the occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections. Data were included from 94 studies.

The researchers found that 20 percent of people who became infected with SARS-CoV-2 remained asymptomatic throughout infection, with a prediction interval of 3 to 67 percent based on 79 studies; some evidence suggested that biases in participant selection influenced the estimate. Thirty-one percent remained asymptomatic in seven studies with defined populations screened for SARS-CoV-2 and followed. Due to heterogeneity, the proportion of people who were presymptomatic could not be summarized. In contacts of people with asymptomatic infection, the secondary attack rate was lower than among those with symptomatic infection (relative risk, 0.35; 95 percent confidence interval, 0.10 to 1.27). Based on modeling studies, the proportion of all SARS-CoV-2 infections resulting from transmission from presymptomatic individuals was higher than from asymptomatic individuals.

“SARS-CoV-2 transmission from people who are either asymptomatic or presymptomatic has implications for prevention,” the authors write. “Social distancing measures will need to be sustained at some level because droplet transmission from close contact with people with asymptomatic and presymptomatic infection occurs.”

One author disclosed financial ties to the pharmaceutical industry.

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