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

Abstract

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.

Keywords: COVID-19; airport; port; quarantine station; travel corridor.

Figure 1.

Flow chart for the selection process of enrolled travelers. Abbreviation: COVID-19, coronavirus disease 2019.

Figure 2.

Time trend of the number of travelers tested for coronavirus disease 2019 (COVID-19) and their percentage of test positivity. A, Time trend of the number of travelers tested by nationality and their percentage of test positivity. B, Time trend of the number of travel corridor users by country.

Figure 3.

Percentage of coronavirus disease 2019 (COVID-19) test positivity at quarantine stations by age and countries and areas. A, Age distribution of the number of travelers tested by sex and the percentage of test positivity. Compared with travelers aged ≥20 years, those aged <20 years showed a low proportion of positive test results, except for those aged 0–2 years, who showed a higher proportion. The higher percentage of positivity among elderly travelers was considered to be due to the small number of travelers tested. B, COVID-19 test positivity at quarantine stations by countries and areas where travelers stayed.