Epidemiology and Risk of Coronavirus Disease 2019 Among Travelers at Airport and Port Quarantine Stations Across Japan: A Nationwide Descriptive Analysis and an Individually Matched Case-Control Study

Tsuboi, Motoyuki; Hachiya, Masahiko; Ohtsu, Hiroshi; Akashi, Hidechika; Miyoshi, Chiaki; Umeda, Tamami

BACKGROUND: The epidemiology and risk of coronavirus disease 2019 (COVID-19) among travelers at international borders remain unclear. METHODS: We conducted descriptive and individually matched case-control studies using a nationwide register for COVID-19 testing of travelers from 3 August to 31 October 2020 at airport/port quarantine stations across Japan. Case patients, defined as travelers positive for COVID-19 on arrival, were individually matched with 4 controls for arrival date and airport or port. We assessed associations between test positivity and traveler characteristics using conditional logistic regression analysis. RESULTS: Overall, 157 507 travelers arriving from 146 countries/areas at 17 quarantine stations across Japan were tested for COVID-19. The percentage of test positivity during the study period was 0.35%. In the case-control study, with 536 case patients and 2144 controls, we found evidence of lower test positivity in travelers aged 3–19 years, female travelers, and travel corridor users (adjusted odds ratio [95% confidence interval], 0.36 [.22–.60], 0.71 [.56–.89], and 0.48 [.30–.77], respectively), whereas higher positivity was associated with arrival from South-East Asia (1.88 [1.33–2.65]) or lower-middle- or low-income countries (2.46 [1.69–3.58] and 7.25 [2.22–23.66], respectively), any symptom (4.08 [1.43–11.65]), and nasopharyngeal compared with saliva sampling (2.75 [1.85–4.09]). A higher 14-day average incidence in the countries of stay was also associated with higher test positivity (1.64 [1.16–2.33] and 3.13 [1.88–5.23] for those from countries and areas where the 14-day average incidence was from 10 to <100 and ≥100 cases per million, respectively). CONCLUSIONS: These findings justify travel restrictions based on the epidemic situation in countries of stay, although underestimation of the epidemic in lower-income countries should be considered. A strict travel corridor could also reduce the risk of COVID-19 importation.