There is high SARS-CoV-2 replication and shedding in the upper respiratory tract during the first week of symptoms, meaning that efficient viral transmission is possible when symptoms are mild and similar to other upper respiratory tract infections (sneezing, runny nose, cough).
Wolfel, R. et al., Virological assessment of hospitalized patients with COVID-2019. Nature (2020). https://doi.org/10.1038/s41586-020-2196-x
1 April 2020
The authors followed the clinical courses of nine confirmed COVID-19 patients without significant underlying disease. They were able to detect and isolate live virus from oro- or nasopharyngeal (throat) swab samples. Peak viral levels occurred around five days after admission, though viral particles were detected in the sputum (spit) even after the respiratory symptoms resolved. These findings suggest most efficient transmission occurs early in the illness when people are experiencing milder symptoms of upper respiratory infection (sneezing, runny nose, cough). Transmission also appears possible after their illness symptoms appear to have resolved, and has implications for discharge management from the hospital. The authors also found active replication of SARS-CoV-2 in the gastrointestinal tract by detection of its specific RNA but were unable to isolate live virus from these samples. These results suggest that infection control procedures should be focused on droplet-based transmission, but further studies into possible feces transmission are needed.
Summary by: Mike Ge