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Eight days after symptoms, COVID-19 not very infectious

May 26, 2020 — 

A local team of scientists, including UM researchers, have found that COVID-19 is not very infectious as soon as eight days after symptoms appear.

In the largest study of its kind to date, the analyses of samples from 90 COVID-19 positive patients in Manitoba found that after just over a week, the ability of the virus to re-infect was low. In fact, the researchers noted: “The probability of obtaining a positive viral culture peaked on day 3 and decreased from that point.”

They note: “These results have implications for clinical care, infection prevention and control and public health. These data can be used to efficiently target case finding efforts by better defining the period of maximal transmission risk. This will be of particular importance in the maintenance phase of the response, where case finding efforts to rapidly interrupt chains of transmission will be essential. Isolation of COVID-19 cases in the community is typically recommended for at least ten days after symptom onset.”

These findings were covered in a CBC story, which reported: “Nonetheless, the larger Winnipeg study allows public-health authorities to be confident in the practice of requiring returning travellers or anyone who may have been exposed to COVID-19 to isolate at home for two weeks, according to the researchers, though the study said larger studies were still needed.”

Lead author of the study is Dr. Jared Bullard [BSc(Med)/04], in the departments of both pediatrics and child health and medical microbiology and infectious diseases in the Rady Faculty of Health Sciences, and associate medical director of Cadham Provincial Laboratory. The study was a joint effort by researchers at Cadham Lab, UM and the National Microbiology Laboratory.

Bullard said: “If somebody’s at home in the community, they typically will be at home for 10 days after those symptoms start, and at that point they’re free to go out and they shouldn’t be infectious to other people. We didn’t have the data to support that and in the hospital we were actually looking at longer.”

Read the entire CBC story here.

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