Background
In August 2021, the U.S. Coast Guard notified the County of San Diego Health and Human Services of persons with COVID-19 symptoms on a 9-day charter fishing trip. We conducted an investigation to identify and rapidly isolate infected persons to reduce the chance of onward transmission.
Methods
Disembarking persons (8 crew; 33 passengers) were asked about COVID-19 symptoms. Anterior nares swabs were collected from everyone except one symptomatic crewmember who sought emergency care. Samples from persons denying symptoms were SARS-CoV-2 rapid antigen tested and submitted for RT-PCR. Samples from symptomatic persons were submitted for RT-PCR to confirm prior positive self-administered antigen testing onboard. Whole-genome sequencing was performed on RT-PCR positive samples with sufficient isolate. Crew, passengers, and tour operator were interviewed to determine mitigation practices used.
Results
Of 41 persons on board, 4 crewmembers reported symptoms. Among 37 asymptomatic persons, 6 (16%) tested positive (2 crew; 4 passengers) on both dockside rapid antigen and RT-PCR, and 5 (14%) tested positive (0 crew; 5 passengers) on RT-PCR only. 15 (37%) of 41 persons on board tested positive. All three symptomatic crewmembers tested by RT-PCR were confirmed positive; the fourth symptomatic crewmember was unavailable for sample collection. Of 14 positive specimens, 10 were suitable for sequencing; all were SARS-CoV-2 Delta variant AY.25. Tour operators observed everyone boarding the vessel self-testing antigen-negative dockside the morning of departure. Vaccination was not required and masks were not routinely worn onboard. Epidemiologic investigation identified crew exposure to an infectious passenger on a tour ending one day before departure.
Conclusion
SARS-CoV-2 spread among crew and passengers during this 9-day cruise after crew exposure to an individual with SARS-CoV-2 infection on a previous cruise. An outbreak response combining dockside rapid antigen testing with isolation and quarantine guidance potentially reduced forward transmission to family members and future passengers.