COVID-19 patients most infectious before, right after symptom onset, study finds

Transmission of COVID-19 is high before and immediately after symptoms begin to show in a person infected with the new coronavirus, a study published in JAMA Internal Medicine shows.

For the study, researchers examined 100 initial patients with confirmed cases of COVID-19 and their contacts in Taiwan. They studied 2,761 close contacts of the 100 initial cases. All close contacts were quarantined at home for 14 days after their last exposure to the initial case.

The overall secondary clinical attack rate (that is, rate of new cases among close contacts) was 0.7 percent.

Researchers found that the attack rate was higher among the 1,818 contacts who were exposed to the initial COVID-19 patients within five days of symptom onset, compared to those who were exposed later. The 299 contacts exposed to the initial COVID-19 patients before their symptoms began were also at higher risk of infection.

"In this study, high transmissibility of COVID-19 before and immediately after symptom onset suggests that finding and isolating symptomatic patients alone may not suffice to contain the epidemic, and more generalized measures may be required, such as social distancing," researchers wrote.



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