COVID-19 most contagious in the few days near symptom onset, study suggests

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COVID-19 may be most infectious in the two days before and three days after symptom onset while patients are mildly or moderately ill, according to research published Aug. 23 in JAMA Internal Medicine. 

The study, led by researchers from the University of Georgia in Athens, involved 730 COVID-19 index patients who were diagnosed between Jan. 8 and July 30, 2020, in Zhejiang Province, China, as well as 8,852 of their close contacts. Close contacts were followed through August. 

Almost 4 percent of close contacts later tested positive. Most were mild or moderate cases, while 18.7 percent were asymptomatic. Close contacts were at highest risk of contracting COVID-19 if they were exposed to an index patient in the two days before and three days after symptom onset, peaking at day zero, findings showed. 

Additionally, researchers found an association between the index patient and close contact's disease severity. 

For example, contacts who were exposed to an index patient with a mild or moderate COVID-19 case were more likely to contract the virus compared to those who were exposed to asymptomatic index patients. Close contacts who tested positive were more likely to be asymptomatic if the index patient was also asymptomatic. 

"Infected contacts of asymptomatic index patients were less likely to present with COVID-19 symptoms, suggesting that quantity of exposure may be associated with clinical presentation in close contacts," researchers said.

To view the full report, click here.

 

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