COVID-19 Infectiousness Found to be Highest in Early Stages of Disease

A recent meta-analysis, published in The Lancet Microbe, has concluded that people who are infected with SARS-CoV-2 seem to be highly infectious within the first week of showing symptoms.

Studies have shown that no live virus has been detected in any type of sample past a nine-day period once symptoms have started. However, SARS-CoV-2 genetic material has been found in both stool and respiratory samples for several weeks, though this cannot cause infection.

The main source of transmission appears to stem from the upper respiratory tract in the early stages of the disease, likely from the onset of symptoms to day five. This is thought to be why it is likely the coronavirus disease 2019 (COVID-19) spreads faster in comparison to SARS-CoV or MERS-CoV.

“This is the first systematic review and meta-analysis that has comprehensively examined and compared viral load and shedding for these three human coronaviruses.” Muge Cevik, MD,of the University of St Andrews, UK, the lead author on the study, said. “It 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.”

The study focused on people who were infected with COVID-19, the majority of which were in the hospital. The researchers calculated the average length of the viral RNA shedding, examining viral load changes and rates of success in isolating the live virus from varying collected samples through the course of an infection. No study which was involved in the systematic review was capable of isolating a live virus beyond nine days of symptom onset.

“These findings suggest that in clinical practice, repeat PCR testing may not be needed to deem that a patient is no longer infectious, as this could remain positive for much longer and does not necessarily indicate they could pass on the virus to others,” Dr Cevik said. “In patients with non-severe symptoms, their period of infectiousness could instead be counted as 10 days from symptom onset.”

The study demonstrates that recommended isolation practices should begin immediately upon noticing the first signs of any symptoms.

To date, this meta-analysis was the most comprehensive one performed on these three particular coronaviruses. The review has provided a more detailed understanding in reference to the viral dynamics of the disease.