key: cord-283467-bgxc3ti8
authors: Wu, Yan; Song, Shujuan; Kao, Qingjun; Kong, Qingxin; Sun, Zhou; Wang, Bing
title: Risk of SARS-CoV-2 infection among contacts of individuals with COVID-19 in Hangzhou, China
date: 2020-06-12
journal: Public Health
DOI: 10.1016/j.puhe.2020.05.016
sha: 
doc_id: 283467
cord_uid: bgxc3ti8

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.

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. January 23, 2020, Zhejiang Province was among the first provinces to declare a major public health emergency and introduced ten policies including vigorously promoting public 2 awareness on epidemic prevention, restricting public gatherings, and taking measures to prevent hospital-acquired infections to prevent the transmission of SARS-CoV-2 infection. 4, 5 After January 27, 2020, the number of imported cases in Hangzhou declined rapidly, and the majority of the cases were local cases, indicating that the prevention and control measures taken had produced effective results. On Continuous data were summarized as medians and interquartile ranges, and t-tests were used for intergroup comparisons. P-values <0.05 were considered to be statistically significant.

The incidence rate of contacts with data collected by field investigation was significantly higher than that of contacts with data collected by big data (5.35% versus 0.07%, P<0.001).

The geographical distribution of close contacts in the districts and counties of Hangzhou is shown in Supplementary Figure S1 . During the observation period, 71 of the 186 (38%)

individuals with symptoms were confirmed to have SARS-CoV-2 infection, of which 54 (76%) had a last exposure-onset interval of <7 days. The incidence rate of SARS-CoV-2 infection in the group with symptoms was significantly higher than that in the group with no symptoms 3 (38.17% versus 0.39%, P<0.05). The most frequently reported abnormal symptoms were cough (39.8%), fever (36.0%), sore throat and rhinorrhea (16.1%). An additional 11 contacts (0.4%) were infected with SARS-CoV-2 but remained asymptomatic. The overall incidence of infection among the contacts was 2.7%.

There was no significant difference in COVID-19 incidence among the close contacts according to age or sex, but significant differences were found according to the level of protection, type of contact, relationship with the index patient, and contact location.

The results in Table 1 show that the infection rate among those living in the same household as the index case was 41.7 times higher than that of individuals who had only had brief contact with the index case. Compared to those who only had brief contact with the index case, those who had dined with the index case had a 2.6 times greater risk of infection, and those who has shared transport, visited, or had contact with the index case in a medical institution had a 3.6 times greater risk of infection. Among the relationships of contacts, family members had the highest risk of infection, with 31.6 times greater risk of infection than healthcare providers or other patients who had been exposed to an index case. In terms of contact locations, the infection rate among those who had contact with the index case in or near his/her home was 17.2 times higher that among those who had contact with the index case in a medical institution; and the infection rate of those who had contact with the index case through work, study, or in a place of entertainment was 6.7 times that among those who had contact with the index case in a medical institution.

This incidence of disease among contacts according to age and sex was consistent with the variation in disease incidence according to age and sex in the population as a whole. 7 The incidence rate among those who wore facemasks was significantly lower than that among those who did not use protective measures (0. In the process of case investigation, the Hangzhou government took full advantage of the big data technology in combination with a grid management mechanism to trace cases, analyze transmission routes, and efficiently collect information of close contacts. Of the contacts identified, 49.4% were identified using big data. This improved the screening efficiency of contacts and reduced the potential for recall bias or intentional concealment. In this way, contact screening was relatively complete. Digitized epidemic prevention and control measures are likely to become more widely used in the future.

Not required (This research does not involve animals and human material and rights.) 

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None declared.