An outbreak of COVID-19 occurred on the Diamond Princess cruise ship in January and February 2020 in Japan . We analysed information on the cases of infection to infer whether airborne transmission of SARS-CoV-2, the causative agent of COVID-19, had occurred between cabins . We infer from our analysis that most infections in passengers started on 28 January and were completed by 6 February, except in those who shared a cabin with another infected passenger . The distribution of the infected cabins was random, and no spatial cluster of the infected can be identified . We infer that the ship's central air-conditioning system for passenger's cabins did not play a role in SARS-CoV-2 transmission, i.e . airborne transmission did not occur between cabins during the outbreak, suggesting that the sufficient ventilation was provided . We also infer that the ship's cabin drainage system did not play a role . Most transmission appears to have occurred in the public areas of the cruise ship, likely due to crowding and insufficient ventilation in some of these areas.