Study population and setting
This study reports temporal patterns of viral shedding in 94 patients with laboratory-confirmed COVID-19 admitted to Guangzhou Eighth People’s Hospital in Guangdong, China between January 21 to February 14, 2020. Participants had at least one positive result (cycle threshold (Ct) value <40) from throat samples, and testing was conducted from symptom onset up to 32 days after onset for clinical monitoring. Additionally, a separate sample of 77 transmission pairs obtained from publicly available sources within and outside mainland China, defined as two confirmed COVID-19 cases identified in the epidemiologic investigation by showing a clear epidemiologic link with each other, such that one case (infectee) was highly likely to have been infected by the other (infector).
Summary of Main Findings
Viral load from throat swabs was highest at the time of symptom onset, and inferred that infectiousness peaked on or before symptom onset. This study suggests that infectiousness started from 2.3 days (95% CI, 0.8–3.0 days) before symptom onset and peaked at 0.7 days (95% CI, −0.2–2.0 days) before symptom onset. Infectiousness was estimated to decline quickly within 7 days of symptom onset, until detection limit was reached at 21 days. Viral load did not differ based on age, sex, or disease severity. The serial interval was estimated to have a mean of 5.8 days (95% CI: 4.8–6.8 days) and a median of 5.2 days (95% CI: 4.1–6.4 days). The study estimated that 44% (95% CI: 25–69%) of secondary cases were infected during the index cases’ pre-symptomatic stage, across a combination of settings with substantial household clustering, active case finding and quarantine outside the home.
This study leverages multiple data sources to understand the temporality of transmission dynamics. Importantly, the study included serial testing among patients with COVID-19 to understand viral load and potential transmissibility throughout the infectious period.
Several limitations should be considered for this study. Symptom onset relies on patient recall after confirmation of COVID-19, leading to potential recall bias. Viral shedding dynamics were based on data from individuals in a hospital setting, which may represent more severe cases. Additionally, individuals were receiving treatment per their respective national protocols, which may have modified viral shedding.
Importantly, this study includes clinical data of serial testing among patients with COVID-19 to understand viral load and potential transmissibility through the infectious period, and potential transmission of pre-symptomatic cases.