Transmission of SARS-CoV-2 during a 2-h domestic flight to Okinawa, Japan, March 2020.

Background: Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2), has rapidly spread globally. Potentially infected individuals travel on commercial aircraft. Thus, this study aimed to investigate and test the association between the use of face masks, physical distance, and COVID-19 among passengers and flight attendants exposed to a COVID-19 passenger in a domestic flight.

Methods: This observational study investigated passengers and flight attendants exposed to COVID-19 on March 23, 2020, on board a flight to Naha City, Japan. Secondary attack rates were calculated. Whole-genome sequencing of SARS-CoV-2 was used to identify the infectious linkage between confirmed cases in this clustering. The association between confirmed COVID-19 and proximity of passengers' seats to the index case and/or the use of face masks was estimated using logistic regression.

Results: Fourteen confirmed and six probable cases were identified among passengers and flight attendants. The secondary attack rate was 9.7%. Twelve of 14 SARS-CoV-2 genome sequences in confirmed cases were identical to that of the index case or showed only one nucleotide mutation. Risk factors for infection included not using a face mask (adjusted odds ratio [aOR]: 7.29, 95% confidence interval [95% CI]: 1.86-28.6), partial face mask use (aOR: 3.0, 95% CI: 0.83-10.8), and being seated within two rows from the index patient (aOR: 7.47, 95% CI: 2.06-27.2).

Conclusion: SARS-CoV-2 was transmitted on the airplane. Nonuse of face masks was identified as an independent risk factor for contracting COVID-19 on the airplane.