MMWR Article Analyzes Cruise Ship Coronavirus Outbreak Response

Novel coronavirus transmission occurred across multiple cruise ship voyages and infected more than 800 people, according to the US Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report.

The CDC’s coronavirus disease 2019 (COVID-19) Response Team and others affiliated with public health agencies analyzed outbreaks on 3 cruise ships in order to detail the public health response to the outbreak on the ships. The study authors said that passengers on cruise ships may be greater than age 65 years, putting them at a greater risk for more severe coronavirus infection.

During February and March, cruise ships were linked to more than 800 laboratory-confirmed coronavirus cases among passengers and crew. There have been 10 reported deaths, the study authors said. The virus spread among voyages from ship to ship via crew members.

The Diamond Princess cruise ship left Japan with about 3700 passengers and crew. The ship made stops in 6 countries and a passenger presenting coronavirus symptoms departed in Hong Kong where he was evaluated and confirmed to have the virus on January 25. By February 3, the ship returned to Japan and was quarantined. Passengers were informed of social distancing practices and monitoring symptoms. By February 5, passengers were quarantined to their cabins but crew remained working, the study authors said. Symptomatic passengers were tested for coronavirus via RT-PCR but later, testing was prioritized for those who were most vulnerable.

From February 16-23, nearly 1000 people left the ship for their home countries, including 329 who returned to the United States. Those from the US entered quarantine or isolation upon their return. There were 111 US citizens (out of 428) that did not return to the US via repatriation flights “either because they had been hospitalized in Japan or for other reasons,” the study authors wrote.

One in 5 of the Diamond Princess passengers or crew had positive test results for SARS-CoV-2 (712 of 3711 aboard). Nearly half were symptomatic at the time of testing. Of the symptomatic patients, nearly 10% required intensive care, and 9 passengers died. And in Japan, 1 nurse, 1 quarantine officer and 1 administrative officer were infected.

As of March 13, a quarter of the US passengers and crew had positive test results for COVID-19 and 11 US passengers remain hospitalized in Japan, including 7 in intensive care, the study authors said.

The Grand Princess cruise ship sailed from San Francisco and made 4 stops in Mexico from February 11-21, the study authors said. Most of the 1111 passengers and crew remained on the ship from the first voyage through a second voyage that departed San Francisco on February 21 with a planned return on March 7. However, on March 4, a California clinician reported 2 patients with COVID-19 who traveled on the first leg of the voyage. The cruise line began canceling group activities on the second leg of the voyage once the CDC notified the company.

On March 5, the study authors documented that a response team was brought to the ship to collect samples from 45 symptomatic passengers and crew. About half had positive test results for SARS-CoV-2 and they were asked to self-quarantine in their cabins.

The boat docked in Oakland on March 8 and passengers and crew were transferred to land-based quarantine sites for 14 days. Those who needed medical attention were given it and the patients were offered SARS-CoV-2 testing.

As of March 21, the study authors reported, there were 469 persons with available test results; 16% of those had positive SARS-CoV-2 test results. The investigators found that 5 crew members from the first leg of the voyage transferred to 3 other ships, totaling 13,317 passengers on board. These ships were told not to sail until the medical logs could be reviewed and crew members tested negative for SARS-CoV-2.

“Following disinfection of the vessel according to guidance from CDC’s Vessel Sanitation Program, remaining foreign nationals will complete quarantine on board,” the study authors added. “The quarantine will be managed by the cruise company, with technical assistance provided by public health experts.”

Overall, the study authors wrote that cases linked to cruise travel have been reported to the CDC in at least 15 states.

The CDC recommended avoiding travel on cruise ships throughout Southeast Asia on February 21. On March 17, the CDC recommended that all cruise travel be deferred worldwide.