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

Abstract

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 health care 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.

Visual Abstract.. Contact Settings and Transmission Risk in Close Contacts of Patients With COVID-19

Risk for transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among close contacts of infected persons has not been well estimated. This study evaluates the risk for transmission of SARS-CoV-2 among a prospective cohort of 3410 close contacts in China exposed to 391 persons with COVID-19 infection according to different settings of exposure.

Figure 1.. Study flow diagram.

CDC = Centers for Disease Control and Prevention; COVID-19 = coronavirus disease 2019; GZCDC = Guangzhou Centers for Disease Control and Prevention; RT-PCR = reverse transcriptase polymerase chain reaction. * Quarantine period was 14 d after the last unprotected contact with confirmed cases and infected persons. † Followed until 6 April 2020.

Figure 2.. Distribution of clusters according to the number of index cases.

In each bar, the light and dark portions indicated the number of index cases outside and inside Guangzhou, respectively.

Appendix Figure 1.. Distribution of quarantine duration among 3410 close contacts and 127 secondary cases.

Day 1 is the start of quarantine. The quarantine period was extended for 337 close contacts in whom reverse transcriptase polymerase chain reaction testing was delayed. COVID-19 = coronavirus disease 2019.

Appendix Figure 2.. Distribution of days from last contact to symptoms onset and quarantine start, and days from symptoms onset to RT-PCR diagnosis among secondary cases.

For days from last contact to symptoms onset, a total of 31 symptomatic cases with symptoms before the last contact and 8 asymptomatic cases were excluded; for days from symptoms to RT-PCR diagnosis, a total of 55 secondary cases who were tested positive on RT-PCR at the first time were further excluded. RT-PCR = reverse transcriptase polymerase chain reaction.