Nearly half of Diamond Princess cruise ship passengers and crew who had coronavirus were asymptomatic when tested, CDC report says

Nearly half of the Diamond Princess cruise ship passengers and crew who tested positive for the novel coronavirus were asymptomatic at the time they were tested, according to a new report from the US Centers for Disease Control and Prevention.

Of the 712 passengers and crew members of the ship who tested positive for coronavirus, 331 — or 46.5% — were asymptomatic at the time of testing, the CDC said.

The agency said that the high rate of asymptomatic infections could partly explain the high rate of infection among cruise ship passengers and crew.

Traces of the virus were found “on a variety of surfaces in cabins of both symptomatic and asymptomatic infected passengers up to 17 days after cabins were vacated on the Diamond Princess but before disinfection procedures had been conducted,” the CDC said.

However, the surface contamination on the ship can’t be used to determine whether transmission occurred from contaminated surfaces without further study, the CDC cautioned.

As of March 13, 107, or 25%, of the 428 Americans on the Diamond Princess tested positive for coronavirus, the agency said.

The CDC’s report also detailed the other cruise ship, the Grand Princess, which was in limbo for days off the coast of California. Of the 469 people with available test results on that ship, 78 — or 17% — of them tested positive for coronavirus.

“The Diamond Princess and Grand Princess had more than 800 total Covid-19 cases, including 10 deaths,” the CDC’s report said.

Between February 3 and March 13, about 200 coronavirus cases in the US were confirmed to be from cruise travelers of multiple voyages, including the Diamond Princess and Grand Princess, the CDC’s report said. This accounted for about 17% of the total reported US cases at the time, according to the report.

“Cases linked with cruise travel have been reported to CDC in at least 15 states,” the report said.