Cruise Ship Travel in the Era of COVID-19: A Summary of Outbreaks and a Model of Public Health Interventions

Background: Cruise travel contributed to SARS-CoV-2 transmission when there were relatively few cases in the United States. By March 14, 2020, the Centers for Disease Control and Prevention (CDC) issued a No Sail Order suspending U.S. cruise operations; the last U.S. passenger ship docked on April 16. Methods: We analysed SARS-CoV-2 outbreaks on cruises in U.S. waters or carrying U.S. citizens and used regression models to compare voyage characteristics. We used compartmental models to simulate the potential impact of four interventions (screening for COVID-19 symptoms; viral testing on two days and isolation of positive persons; reduction of passengers by 40%, crew by 20%, and port visits to one) for 7-day and 14-day voyages. Findings: During January 19–April 16, 2020, 89 voyages on 70 ships had known SARS-CoV-2 outbreaks; 16 ships had recurrent outbreaks. There were 1,669 RT-PCR-confirmed SARS-CoV-2 infections and 29 confirmed deaths. Longer voyages were associated with more cases (adjusted incidence rate ratio, 1·10, 95% CI: 1·03-1·17, p < 0.0001). Mathematical models estimated a 70-78% reduction in transmission for 7-day vs. 14-day voyages. On 7-day voyages, the most effective interventions were reducing the number of individuals onboard (43-49% reduction in total infections) and testing passengers and crew (42-43% reduction in total infections). Results were similar for 14-day voyages. All four interventions reduced transmission by 80%, but no single intervention or combination eliminated transmission. Interpretation: SARS-CoV-2 outbreaks on cruises were common during January-April 2020.  Despite all interventions modelled, cruise travel still poses a significant SARS-CoV-2 transmission risk. Funding: CDC. Declaration of Interests: The authors have no interests to declare. Ethics Approval Statement: This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy (See e.g., 45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. §241(d); 5 U.S.C. §552a; 44 U.S.C. §3501 et seq.). Passenger-level data were deidentified and analysed at the voyage-level.