Study: Coronavirus patients most infectious 3 days before displaying symptoms

By Han Guo

A recent study has shown that patients with coronavirus are highly infectious three days prior to displaying symptoms, during the so-called ‘incubation period’.

The incubation period is the time between exposure to an infection, and the appearance of the first symptoms. Research estimates the average incubation period of coronavirus is 4.9 days.

A diagram displaying the likelihood of infection after contact with infected patients

The infection curve showed that 73.0% of secondary cases were infected before symptoms appeared. This was most prominent during the last three days of the incubation period. Therefore, risk of infection is strongest in the first three days before fever begins.

The study assessed the potential for transmission of 50 infection clusters, including 124 patients during the incubation period.

All secondary cases had been in contact with first generation cases before symptoms appeared.

The study is from the paper published by Huazhong University of Science and Technology called “Transmission of coronavirus disease 2019 during the incubation period may lead to a quarantine loophole.”

Researchers recommend that once a confirmed case is identified, all close contacts must be traced back at least three days before the onset of symptoms. These contacts should then be isolated.