More than 800 cases of laboratory-confirmed COVID-19 infections occurred during outbreaks on three cruise ship voyages from around the world, resulting in the deaths of at least 10 people. After evacuating previously quarantined ships, infectious disease experts found SARS-CoV-2, the virus responsible for the respiratory disease, on ship surfaces more than two weeks after the vessels were vacated.
“SARS-CoV-2 RNA was identified 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 Centers for Disease Control and Prevention (CDC) said in a special report. However, the agency cautions that current data cannot be used to determine whether transmission occurred from contaminated surfaces.
An estimated 30 million passengers are transported on less than 300 cruise ships around the world every year, according to a 2019 report by Cruise Lines International Association. Cruises bring together diverse populations living in close proximity for extended periods of time, which helps facilitate the spread of infectious viruses like SARS-CoV-2.
“Cruise ships are often settings for outbreaks of infectious diseases because of their closed environment, contact between travelers from many countries, and crew transfers between ships,” the report notes.
Between February and March 2020, COVID-19 outbreaks were associated with three cruise ship voyages. A majority of the passengers were asymptomatic, furthering the spread of the virus not just between people aboard the ship but also into the communities that they visited and health officials who responded to the crisis once notified. In some cases, transmission largely occurred before the quarantine was implemented. Of particular interest to the CDC are two cruise ships, the Diamond Princess and the Grand Princess.
With more than 3,700 passengers and crew, the Diamond Princess was home to the largest cluster of COVID-19 cases outside of China for nearly two weeks last month. It came five days after setting sail on January 20 when an asymptomatic passenger departed the ship in Hong Kong and tested positive for the virus. A week later, the ship returned to Japan but made six stops in three countries along the way before being quarantined at the port of Yokohama, Japan. Nearly half of those aboard the ship were asymptomatic at the time of testing; about one-in-10 eventually required intensive care and nine passengers died as a result of their infection.
Nineteen cases were identified in cruise-goers aboard the Grand Princess, which sailed on a roundtrip from San Francisco and made four stops in Mexico. Confirmation of COVID-19 aboard the ship prompted health officials to quarantine individuals and restrict the ship from docking in the Bay Area for several days. A response team sent to the ship collected samples via a helicopter, later revealing nearly half of all aboard the ship tested positive for the virus.
Collectively, the two ships accounted for more than 800 known cases and 10 deaths.
On March 13, Cruise Lines International Association announced a 30-day voluntary suspension on US cruise operations. The CDC warns that “aggressive efforts” are needed to contain the spread and advises people to forego cruise travel around the world during the COVID-19 pandemic.