In addition to the environmental persistence of SARS-CoV-2, the amount of virus entering the environment and number of viruses required to cause infection (infectious dose) may influence the likelihood of transmission. 

Generally, the greater the amount of pathogen entering the environment (e.g. when an infected individual sneezes, coughs, or defecates), the greater the risk of exposure or contact with that pathogen.

Currently, there are no measures of the concentration of live, infectious SARS-CoV-2 shed in faeces or the duration of shedding. The concentration of SARS-CoV-2 genetic material in stool can vary widely among different individuals as well as over the course of the disease in a single individual. There is currently no evidence that presence or concentration of SARS-CoV-2 genetic material in stool is influenced by disease severity or even the presence of symptoms. The duration of shedding of SARS-CoV-2 genetic material has not been fully characterized and may begin 3-5 days prior to symptom onset and persist for days to weeks after symptoms begin (Study 1, Study 2, Study 3). Future research should measure the concentration and duration of shedding of viable, infectious SARS-CoV-2 in faeces from individuals with a range of symptoms and disease severities.

The number of viruses needed to cause infection in the majority of people (known as the infectious dose) is not known for SARS-CoV-2. Generally, the lower the infectious dose, the higher the risk of transmission. This section will be updated as we learn more about the shedding patterns in stool and the infectious dose. 

Author: Jackie Knee

Review: Tom Heath, Robert Dreibelbis, Oliver Cumming, Karin Gallandat, Kate Medlicott
Last update: 13.08.2020