- COVID-19 transmission is estimated to start at least 2 days before symptom onset, based on viral shedding and epidemiological data from China.
- 44% of disease transmission is estimated to be presymptomatic.
- Infectiousness may decline abruptly at about 1 week.
Why this matters
- This substantial level of presymptomatic transmission far exceeds the rate of 6% reported for Singapore.
- These findings suggest a need for shifts in disease-control measures, including contact tracing, to 2-3 days before symptom onset.
- Temporal patterns of viral shedding were determined based on viral load clinical data for 94 patients with laboratory-confirmed COVID-19.
- Viral load data were combined with epidemiological data from 77 transmission pairs (one person likely infected the other) on incubation period and serial interval between cases in the transmission chain.
- Funding: Department of Science and Technology of Guangdong Province; other.
- Infectiousness (using viral load data) began 2.3 days and peaked 0.7 days before symptom onset.
- Infectiousness was estimated to decline abruptly within 7 days.
- Presymptomatic transmission accounted for 44% of transmissions.
- Viral load data did not vary by sex, age group, or disease severity.
- Potential for recall bias.
- Small sample size.