• clinical epidemiology
• infection control
• respiratory infection
• viral infection

Cruise ships, with their unique enclosed environment, have provided valuable insights into the dynamics of viral transmission during the COVID-19 pandemic. On the Diamond Princess cruise ship in Yokohama, Japan, approximately 21% of those on board tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with 51.7% of these representing asymptomatic infections at the time of testing.1 In this month’s edition of Thorax, Ing et al describe an outbreak on a cruise ship departing Argentina for the Antarctic peninsula with 223 members, all of whom were screened with temperature and symptom check prior to embarkation in mid-March 2020. At day 8, the first member developed symptoms. Despite immediate imposition of cabin isolation of all passengers and strict personal protective equipment use by crew, 128 (59.0%) of those on board tested positive for SARS-CoV-2 on day 20, when everyone was screened with an RT-PCR-based test. Of those testing positive, only 24 (18.8%) developed symptoms and 104 (81.2%) remained asymptomatic until day 28, when the first cohort of passengers disembarked. Some caution is required in interpreting this figure as the follow-up period is not long enough to be confident that all individuals remained truly asymptomatic. Nevertheless, it is striking that despite rigorous attempts to limit spread, such widespread transmission occurred on board. The enclosed environment may be the major driver of the high transmission rate; however, the possibility that transmission from …