Imamura, et al. (2023) describe the characteristics of COVID-19 transmission within different social settings and evaluate settings associated with onward transmission to other settings.

This is a case series study of laboratory-confirmed COVID-19 cases in Tokyo between January 23 and December 5, 2020, when vaccination was not yet implemented. Using epidemiological investigation data collected by public health centers, epidemiological links were identified and classified into 7 transmission settings: imported, nightlife, dining, workplace, household, health care, and other.

Of the 44,054 confirmed COVID-19 cases in this study, 25,241 (57.3%) were among male patients, and the median (IQR) age of patients was 36 (26-52) years. Transmission settings were identified in 13,122 cases, including 6768 household, 2733 healthcare, and 1174 nightlife cases. More than 6600 transmission settings were detected, and nightlife (72 of 380 [18.9%]; P < .001) and healthcare (119 [36.2%]; P < .001) settings were more likely to involve 5 or more cases than dining, workplace, household, and other settings. Nightlife cases appeared in the earlier phase of the epidemic, while household and healthcare cases appeared later. After adjustment for transmission setting, sex, age group, presence of symptoms, and wave, household and healthcare cases were less likely to generate onward transmission compared with nightlife cases (household: adjusted odds ratio, 0.03; 95% CI, 0.02-0.05; healthcare: adjusted odds ratio, 0.57; 95% CI, 0.41-0.79). Household settings were associated with intergenerational transmission, while non-household settings mainly comprised transmission between the same age group. Among 30,932 cases without identified transmission settings, cases with a history of visiting nightlife establishments were more likely to generate onward transmission to non-household settings (adjusted odds ratio, 5.30 [95% CI, 4.64-6.05]; P < .001) than those without such history.

In this case series study, COVID-19 cases identified in nightlife settings were associated with a higher likelihood of spreading COVID-19 than household and healthcare cases. Surveillance and interventions targeting nightlife settings should be prioritized to disrupt COVID-19 transmission, especially in the early stage of an epidemic.

Reference: Imamura T, et al. Transmission of COVID-19 in Nightlife, Household, and Health Care Settings in Tokyo, Japan, in 2020. JAMA Netw Open. 2023;6(2):e230589. doi:10.1001/jamanetworkopen.2023.0589