COVID-19 on Cruise Ships, February–March 2020: Diamond Princess, Grand Princess and Beyond

About 30 million passengers travel on 272 cruise ships worldwide each year. Ships bring many people together for days in a closed space, which helps respiratory illness spread — and passengers on some voyages are 65 or older, at greater risk from COVID-19. In February–March 2020, outbreaks tied to three cruise voyages caused more than 800 laboratory-confirmed cases among passengers and crew, including 10 deaths, and the virus passed across several voyages of several ships.

Timeline

Diamond Princess

The ship left Yokohama on January 20 with about 3,700 people aboard: 1,045 crew (median age 36) and 2,666 passengers (median age 69) — crew from 48 nations and passengers from 36, 1,281 of them from Japan and 416 from the United States. On January 25 a passenger with symptoms left the ship in Hong Kong and tested positive. The ship returned to Japan on February 3, after six stops in three countries, and was quarantined.

• From February 5, passengers were confined to their cabins; crew kept working, so they could not be isolated.
• People with symptoms and their contacts were tested first; anyone positive was taken off and hospitalized. Testing then widened, prioritizing older people, those with underlying conditions, and those in inside cabins with no outdoor access.
• From February 16 to 23, nearly 1,000 people were flown home, 329 of them to the United States, into quarantine or isolation. Others finished a 14-day quarantine on board or on land.
• CDC used temporary "Do Not Board" orders to keep travelers off commercial flights to the United States, and the State and Homeland Security departments restricted entry of non-U.S. travelers.

Results: of 3,711 people, 712 (19.2%) tested positive — 331 (46.5%) of them with no symptoms when tested. Of 381 with symptoms, 37 (9.7%) needed intensive care; nine people died. Three Japanese responders were also infected. As of March 13, 107 of the 428 U.S. passengers and crew had tested positive, and 11 were still hospitalized in Japan.

Cumulative confirmed COVID-19 cases by date of detection, Diamond Princess, Yokohama, February 3–March 16, 2020. CDC / MMWR

Grand Princess

The ship made a round trip from San Francisco to Mexico from February 11 to 21 (voyage A). Most of its 1,111 crew and 68 passengers stayed on for voyage B, leaving February 21 with 2,460 passengers, 2,008 of them from the United States.

• On March 4, a California clinician reported two voyage-A travelers with COVID-19 symptoms, one confirmed; more than 20 more voyage-A cases followed, mostly in California, with one death.
• On March 5, a team was flown by helicopter to the ship and tested 45 people with symptoms: 21 were positive — 2 passengers and 19 crew.
• Passengers and sick crew stayed in their cabins, with room service replacing dining rooms. After docking in Oakland on March 8, people went to land-based quarantine or isolation for 14 days; of 469 tested by March 21, 78 (16.6%) were positive.
• On February 21, five voyage-A crew had moved to three other ships carrying 13,317 passengers; CDC issued no-sail orders until medical logs were checked and the five tested negative.

Beyond the two ships

From February 3 to March 13, about 200 COVID-19 cases in the United States — roughly 17% of all U.S. cases at the time — were among returned cruise travelers, reported from at least 15 states, including at least 60 from Nile River cruises in Egypt. Some passengers then infected others at home.

Cruise ships with COVID-19 cases requiring public health responses, worldwide, January–March 2020. CDC / MMWR

Lessons

• Ships breed outbreaks: a closed setting, travelers from many countries, and crew moving between ships. On the Diamond Princess, passengers were mostly infected before quarantine, while crew infections peaked after it; on the Grand Princess, crew infected on voyage A likely passed the virus to voyage B's passengers.
• Many infections were silent — nearly half without symptoms when tested. Models of the Diamond Princess suggest 17.9% of infected people never developed symptoms, which may help explain the high attack rate.
• Virus RNA was found on surfaces in infected passengers' cabins up to 17 days after they left, before cleaning — not proof of spread by surfaces, but worth studying.
• Responses took extensive resources and coordination among U.S. agencies, foreign health ministries and embassies, state and local health departments, hospitals, labs and cruise companies.

CDC's advice at the time: everyone should defer all cruise travel worldwide during the pandemic.

Sources

Based on Moriarty LF, Plucinski MM, Marston BJ, et al., "Public Health Responses to COVID-19 Outbreaks on Cruise Ships — Worldwide, February–March 2020," MMWR Morbidity and Mortality Weekly Report, volume 69 (as corrected), first posted March 23, 2020, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The report's percentage for Diamond Princess deaths does not fit the group it describes, and its counts of U.S. travelers flown home do not reconcile, so only counts are given here.