CDC: Cruise Ship Outbreaks Risk Spreading COVID-19 "Beyond the Voyage"

In  a study released Monday, the U.S. Centers for Disease Control and Prevention (CDC) reported the results of an analysis of more than 800 COVID-19 cases aboard two cruise ships. The paper's authors concluded that outbreaks aboard cruise ships pose a risk of "rapid spread of the disease beyond the voyage."

Cases linked with cruise travel have been reported to the CDC in at least 15 states, and multiple international cruises have been implicated in reports of COVID-19 cases - as seen recently with the outbreak aboard Ruby Princess. The authors advised that "all persons should defer all cruise travel worldwide during the COVID-19 pandemic," reflecting current guidance from the CDC and the U.S. State Department.

The analysis centered on one voyage of the cruise ship Diamond Princess and two voyages of the Grand Princess. The outbreak aboard Diamond Princess may be the best-known instance: about 700 cases occured among the 3,700 passengers and crew on board, an attack rate of about 20 percent. 428 cases were American citizens or permanent residents, and 11 of them are still hospitalized in Japan. Nine individuals have died to date. 

Notably, nearly half of the passengers and crew who tested positive on board the Diamond Princess had asymptomatic infections at the time of testing - that is, their condition would not raise flags during a standard clinical screening exam, even though they had the disease. "A high proportion of asymptomatic infections could partially explain the high attack rate among cruise ship passengers and crew," the authors wrote. 

Additionally, the SARS-CoV-2 virus RNA was identified on surfaces in the cabins of people who tested positive - both those with symptoms and without - up to 17 days after their cabins had been vacated but not cleaned. Later examination showed that the presence of these RNA fragments did not indicate the presence of viable virus. 

Japanese study shows pattern of infection

A report released March 18 by four scientists with Japan's National Institute of Infectious Diseases determined that aboard Diamond Princess, the disease appeared to spread early among food service crewmembers, then to crewmembers who shared cabins or were berthed in the same area. 

"Interviews indicated that infection had apparently spread among persons whose cabins were on the same deck . . . and who worked in the same occupational group (food service), probably through contact or droplet spread, which is consistent with current understanding of COVID-19 transmission," the authors found. "Eight of 20 crew members with confirmed COVID-19 had cabin mates; investigators later learned that following disembarkation . . . five of the eight cabin mates had also developed COVID-19."