Detection and viral RNA shedding of SARS-CoV-2 in respiratory specimens relative to symptom onset among COVID-19 patients in Bavaria, Germany

Abstract

We assessed SARS-CoV-2 RT-PCR diagnostic sensitivity and Cycle threshold (Ct) values relative to symptom onset in symptomatic COVID-19 patients from Bavaria, Germany, of whom a subset were repeatedly tested. Locally Weighted Scatterplot Smoothing (LOWESS) method was used to assess the relationship between symptom onset and Ct-values. Kaplan Meier plots were used to visualize the empirical probability of detecting viral RNA over time and estimate the time until clearance of viral RNA among the repeatedly tested patients. Among 721 reported COVID-19 cases, the viral RNA was detected in specimens taken between three days before and up to 48 days after symptom onset. Mean Ct-value was 28.6 (95%CI: 28.2-29.0) with the lowest mean Ct-values (26.2) observed two days after symptom onset. Up to 7 days after symptom onset, the diagnostic sensitivity of the RT-PCR among repeatedly sampled patients (n = 208) remained above 90% and decreased to 50% at day 12 (95%CI: 10.5-21.5). Our data provide valuable estimates to optimize the timing of sampling of individuals for SARS-CoV-2 detection. A considerable proportion of specimens sampled before symptom onset had Ct-values comparable with Ct-values after symptom onset, suggesting the probability of presymptomatic transmission.