Alliance for Pandemic Preparedness

August 14, 2020

Contact Settings and Risk for Transmission in 3410 Close Contacts of Patients With COVID-19 in Guangzhou, China: A Prospective Cohort Study

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  • A study of SARS-CoV-2 infection among 3,410 close contacts of 391 confirmed SARS-CoV-2 cases in Guangzhou, China found a secondary attack rate of 4%. Close contact was defined as contact without effective protection starting 2 days before symptom onset or 2 days before testing for asymptomatic cases. Eight percent of index cases were asymptomatic, 16% had mild symptoms, 69% had moderate symptoms, and 9% had severe/critical illness. Secondary attack rates were highest in household settings (10%) and lower in healthcare settings (1%) and on public transportation (0.1%).  
  • Secondary attack rate was positively associated with index case severity, at 0.3% for asymptomatic index cases, 3% for mild cases, 6% for moderate cases, and 6% for severe or critical cases. Secondary attack rate was also far higher for index cases with a productive cough (14% versus 3%).  

Luo et al. (Aug 2020). Contact Settings and Risk for Transmission in 3410 Close Contacts of Patients With COVID-19 in Guangzhou, China: A Prospective Cohort Study. Annals of Internal Medicine. https://doi.org/10.7326/M20-2671