Cruise ship travel and the spread of COVID-19 - Australia as a case study

Introduction: Cruise ship linked COVID-19 outbreaks have been identified as a potential source of community transmission of COVID-19 in Australia and worldwide. The risk factors and potential mitigation around COVID-19 infections on cruise ships and communities is a research gap. Methods: A correlation and regression analyses for risk factors for COVID-19 attack rates oncruise ships worldwide with reported COVID-19 from January 1, 2020 to May 11, 2020 were performed, with a more detailed analysis done for Australia. Geospatial emerging hot spot analysis during key time periods was used to assess temporal trends in spatial clustering of COVID-19 cases related to two cruise ship events in NSW, Australia. Results: For 36 cruise ships with global COVID-19 cases, available cabins had a moderate inverse correlation with the attack rate (-0.4154; 95% CI [-0.0002, -0.00003], P < 0.0118). The number of cabins, the number of decks with cabins, and passenger-to-space ratio were significantly associated with attack rate, however, the duration at sea was not. By May 2020, cruise ship passengers made up 14.9% of COVID-19 cases in Australia and 27% of the COVID-19 related deaths. Emerging hot spots of community transmission in Sydney occurred during 1-2 incubation periods of two cruise ship events. Conclusion: Mitigation of risk on cruise ships should focus on spatial design and reducing crowding, including rapid surveillance and on-board testing. To mitigate this risk during the era of COVID-19, all passengers disembarking an infected ship should be quarantined for at least the 14-day window period and tested for COVID-19, regardless of symptoms. Vaccination should be a pre-requisite for travel of any kind once available.