Abstract Objectives This study determined the rate of secondary infection among contacts of individuals with confirmed COVID-19 in Hangzhou according to the type of contact, the intensity of the contact, and their relationship with the index patient. Study design Retrospective cohort study. Methods The analysis used the data of 2,994 contacts of 144 individuals with confirmed SARS-CoV-2 infection. The contacts were categorized according to the information source, type of contact, location, intensity of contact, and relationship with the index patient. Results The incidence of infection differed significantly according to contact type. Of the contacts, 186 (6.2%) developed symptoms and 71 (2.4%) had confirmed infection with SARS-CoV-2. The main symptoms were cough and fever. Compared to those who had brief contact with the index case, those who had dined with the index case had a 2.6 times greater risk of infection; those who had shared transport, visited, or had contact with the index case in a medical institution had a 3.6 times greater risk of infection; and household contacts had 41.7 times greater risk of infection. Family members had a 31.6 times greater risk of infection than healthcare providers or other patients exposed to an index case. Conclusions The form and frequency of contact are the main factors affecting the risk of infection among contacts of individuals with COVID-19. Centralized isolation and observation of close contacts of individuals with confirmed SARS-CoV-2 infection, in addition to population-based control measures, can reduce the risk of secondary infections and curb the spread of the infection.
Risk of SARS-CoV-2 infection among contacts of individuals with COVID-19 in Hangzhou, China