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

BACKGROUND: Risk for transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to close contacts of infected persons has not been well estimated OBJECTIVE: To evaluate the risk for transmission of SARS-CoV-2 to close contacts in different settings DESIGN: Prospective cohort study SETTING: Close contacts of persons infected with SARS-CoV-2 in Guangzhou, China PARTICIPANTS: 3410 close contacts of 391 index cases were traced between 13 January and 6 March 2020 Data on the setting of the exposure, reverse transcriptase polymerase chain reaction testing, and clinical characteristics of index and secondary cases were collected Measurement: Coronavirus disease 2019 (COVID-19) cases were confirmed by guidelines issued by China Secondary attack rates in different settings were calculated RESULTS: Among 3410 close contacts, 127 (3 7% [95% CI, 3 1% to 4 4%]) were secondarily infected Of these 127 persons, 8 (6 3% [CI, 2 1% to 10 5%]) were asymptomatic Of the 119 symptomatic cases, 20 (16 8%) were defined as mild, 87 (73 1%) as moderate, and 12 (10 1%) as severe or critical Compared with the household setting (10 3%), the secondary attack rate was lower for exposures in healthcare settings (1 0%;odds ratio [OR], 0 09 [CI, 0 04 to 0 20]) and on public transportation (0 1%;OR, 0 01 [CI, 0 00 to 0 08]) The secondary attack rate increased with the severity of index cases, from 0 3% (CI, 0 0 to 1 0%) for asymptomatic to 3 3% (CI, 1 8% to 4 8%) for mild, 5 6% (CI, 4 4% to 6 8%) for moderate, and 6 2% (CI, 3 2% to 9 1%) for severe or critical cases Index cases with expectoration were associated with higher risk for secondary infection (13 6% vs 3 0% for index cases without expectoration;OR, 4 81 [CI, 3 35 to 6 93]) LIMITATION: There was potential recall bias regarding symptom onset among patients with COVID-19, and the symptoms and severity of index cases were not assessed at the time of exposure to contacts CONCLUSION: Household contact was the main setting for transmission of SARS-CoV-2, and the risk for transmission of SARS-CoV-2 among close contacts increased with the severity of index cases PRIMARY FUNDING SOURCE: Guangdong Province Higher Vocational Colleges and Schools Pearl River Scholar Funded Scheme