Mar 24, 2020 - Health

Coronavirus traces found on Diamond Princess 17 days after passengers left

 Emergency workers in protective clothing exit the Diamond Princess cruise ship in Yokohama, Japan.
Emergency workers exit the Diamond Princess cruise ship in Yokohama, Japan, in February. Photo: Carl Court/Getty Images

Traces of the novel coronavirus were found in the cabins on the Diamond Princess cruise ship up to 17 days after passengers left, a study published by the CDC Monday found.

Why it matters: Axios health care editor Sam Baker notes: "The virus lives a long time on hard surfaces, and that's another reason to be wary about quickly reopening businesses like bars, restaurants and gyms while the virus is still spreading quickly."

  • Per the CDC, "Although these data cannot be used to determine whether transmission occurred from contaminated surfaces, further study of fomite transmission of SARS-CoV-2 aboard cruise ships is warranted."
COVID-19 on cruise ships poses a risk for rapid spread of disease, causing outbreaks in a vulnerable population, and aggressive efforts are required to contain spread."
— CDC statement in study

How it works: The study examined coronavirus outbreaks aboard the Carnival-owned cruise ships the Diamond Princess, which was quarantined off Yokohama, Japan, last month, and the Grand Princess, which was stranded off the San Francisco coast for several days.

What they found: Per the CDC, "By March 17, confirmed cases of COVID-19 had been associated with at least 25 additional cruise ship voyages."

  • 46.5% of cases from the Diamond Princess were asymptomatic when tested, which could "partially explain the high attack rate among cruise ship passengers and crew," the CDC said. The virus infected 712 of the 3,711 people aboard the ship — 19.2% of those on board.
  • On the Grand Princess, 19 crew members and two passengers initially tested positive for the virus. The CDC study states the ship's outbreak was linked to 78 cases as of Saturday.

Between the lines: Tara Smith, an infectious disease professor and epidemiologist, reacted to the study by noting in a Twitter thread that the "asymptomatic" number was given at the time of testing. "They didn't report follow-up to show how many eventually developed symptoms," Smith said. "So many possibly still in incubation period."

  • "In the Discussion they add this: 'Available statistical models of the Diamond Princess outbreak suggest that 17.9% of infected persons never developed symptoms' — so based on models, and not the 'half of those tested were asymptomatic' that I've already seen reported," Smith added.

The bottom line: Per Smith, while SARS-CoV-2 RNA was "identified on a variety of surfaces in cabins of both symptomatic & asymptomatic infected passengers up to 17 days after cabins were vacated" and before the vessel had been fully disinfected, "viral RNA doesn't necessarily mean live virus was present."

Of note: A study published last Tuesday in the New England Journal of Medicine found that SARS-CoV-2 stays viable in the air for several hours and can last on surfaces for up to three days.

Flashback: The outbreak aboard the Diamond Princess prompted countries including the U.S. to evacuate citizens who were aboard the ship.

  • An elderly patient tested positive for COVID-19 after disembarking from the Grand Princess.

Read the CDC study:

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