Viral load most important factor in COVID-19 transmission

The amount of virus in the noses and throats of COVID-19 patients is the most important factor in determining whether they will infect others, according to a report published on Tuesday in The Lancet Infectious Diseases.

Researchers in Spain studied 282 patients and 753 of their recent close contacts. While household members most often became infected, the viral load “was the most important factor in determining whether transmission occurred between a case and their contacts,” said coauthor Michael Marks of the London School of Hygiene & Tropical Medicine.

“Whether the case was coughing or had other symptoms didn’t seem to play a major role,” he said, reinforcing that even patients without symptoms need to isolate themselves.

He said health authorities might want to consider more enhanced contact tracing for individuals with higher viral loads.

A separate study by UK researchers, which has not yet been peer-reviewed, reported similar findings.