When is a person with COVID-19 most infectious? | Health Info

By Robert Preidt, Health Day reporter

FRIDAY, August 27, 2021 (HealthDay News) – New research answers a burning question: When are COVID-19 patients most infectious?

The answer? Two days before and three days after they develop symptoms.

The results underscore the importance of rapid testing and quarantine if someone feels sick, the study’s authors said.

The researchers also found that those infected are more likely to be asymptomatic if they caught the virus from a primary case (the first person infected in an outbreak) that was also asymptomatic.

“In previous studies, viral load has been used as an indirect measure of transmission,” said study co-leader Dr Leonardo Martinez, assistant professor of epidemiology at the School of Public Health. Boston University.

“We wanted to see if the results of these previous studies, which show that COVID cases are most transmissible a few days before and after symptoms appear, could be confirmed by looking at secondary cases among close contacts,” said Martinez in a college press release.

For the study, Martinez and colleagues analyzed data from about 9,000 close contacts of primary cases in China’s Zhejiang province from January 2020 to August 2020. This was before the advent of the even more contagious Delta variant. .

Close contacts included people who lived in the same household or had dinner together, co-workers, people in hospitals and drivers of shared vehicles. They were monitored for at least 90 days after the first positive results of their COVID-19 test.

Of the primary cases, 89% developed mild or moderate symptoms, 11% were asymptomatic, and none developed severe symptoms.

Household contacts of primary cases and people who were exposed to primary cases repeatedly or for longer periods of time had higher infection rates than other close contacts, the results showed.

But all close contacts were more likely to be infected with the primary case if they were exposed shortly before or after that person developed symptoms, according to the study published online August 23 in JAMA Internal Medicine.

Compared to mild and moderate symptomatic primary cases, those who were asymptomatic were much less likely to infect close contacts. If they did, the contacts were also less likely to have visible symptoms, the researchers reported.

“Our results suggest that the timing of exposure versus symptoms in primary cases is important for transmission, and this understanding provides further evidence that rapid testing and quarantine after a person feels sick is a critical step. to control the outbreak, ”Martinez said. “This study further underscores the need for vaccination, which reduces clinical severity in people who develop COVID. “

The United States Centers for Disease Control and Prevention has more information on COVID-19[feminine.

SOURCE : Boston University School of Medicine, communiqué de presse, 26 août 2021

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