TUESDAY, Aug. 30, 2022 (HealthDay News) — Twenty percent of COVID-19 cases shed infectious virus before symptom onset, according to a study published online Aug. 18 in The Lancet Respiratory Medicine.

Seran Hakki, Ph.D., from Imperial College London, and colleagues conducted a prospective, longitudinal, community cohort of contacts of newly diagnosed confirmed severe acute respiratory syndrome coronavirus 2 index cases. Infectiousness among household- and non-household-exposed contacts aged 5 years or older was characterized across the full course of infection. Data were included for 57 people who were at the start of infection; the onset and end of infectious viral shedding were captured for 42 cases.

The researchers found that the median duration of infectiousness was five days. Sixty-three percent of 38 cases had detectable virus before symptom onset, but only seven of 35 cases shed infectious virus presymptomatically. Onset of symptoms was a median of three days before peak viral RNA and peak infectious viral load. Sixty-five and 24 percent of 34 cases continued to shed infectious virus five and seven days after symptom onset, respectively (survival probabilities, 67 and 35 percent, respectively). Poor correlation was seen for lateral flow device results with infectious viral shedding during the viral growth phase, but correlation was high during the decline phase (sensitivity, 67 and 92 percent, respectively).

“Preliminary evidence from our study has already informed policy and the real-world evidence presented here could be used to improve infection control policies and optimize guidance on self-isolation to minimize secondary transmission,” the authors write.

One author disclosed financial ties to Janssen and Takeda.

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