A systematic review and meta-analysis of three human coronaviruses suggest that people infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are likely to be most infectious in the first week after symptom onset, highlighting the need to identify and isolate cases early.
The study findings, published in the Lancet Microbe, suggest SARS-CoV-2 viral load peaks in the upper respiratory tract early in the disease course, from symptom onset to day five, whereas SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) viral load peaks later, providing the likely explanation for why COVID-19 spreads more rapidly in the community.
The evidence so far on SARS-CoV-2 points to a pattern of a nine-day period of infectiousness. As the study only looked at confirmed cases and not those who may have been exposed, it is unable to provide insight into the recommended duration of quarantine.
Although viral loads appear to be similar between people infected with SARS-CoV-2 who develop symptoms and those who do not, most studies indicate that asymptomatic individuals may clear the virus faster from their body and might be infectious for a shorter amount of time.
Although SARS-CoV-2 genetic material may still be detected in respiratory or stool samples for several weeks, no live virus was found in any type of sample collected beyond nine days from symptom onset.
The authors concluded that people with SARS-CoV-2 are mostly likely to be highly infectious in the first five days following symptom onset.
Lead author Dr Muge Cevik of the University of St Andrews, Fife, UK, said the study provides a clear explanation for why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is so much more difficult to contain.
She said we need to raise public awareness about the range of symptoms linked with the disease, including mild symptoms that may occur earlier in the course of the infection.