Genetic Study Shows How Coronavirus Swept Princess Diamond

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The destination of more than 3,600 passengers and crew quarantined on the cruise Diamond princess made headlines in the first few weeks of the coronavirus pandemic in February.

An outbreak on board the ship eventually led to nearly 700 infections and seven deaths from COVID-19.

Now, a genetic flashback to the events shows that the outbreak likely originated from a single infected person, and the virus spread rapidly as people mingled in crowded onboard events, Japanese researchers report.

However, one thing is certain: quarantine and containment measures enacted after the virus was discovered limited cases and likely saved lives.

The first known case of coronavirus infection in the Diamond princess It was reported on February 1 in an 80-year-old sick passenger who left the ship in Hong Kong on January 25.

As of February 4, there was a quarantine throughout the ship and passengers were largely restricted to their staterooms.

At that time, the incidence of new cases “abruptly decreased,” according to a team led by Makoto Kuroda of the National Institute of Infectious Diseases in Tokyo.

This indicates that “the movement restriction policy was very successful in greatly reducing the number of secondary transmissions on board the Diamond princess“the researchers reported.

A previous study had also estimated that quarantine and other public health measures “prevented more than 2,000 additional cases” on board the Diamond princessCompared to doing nothing at all, Kuroda’s group noted.

In the new study, the Japanese team sought to determine the origins of the cruise outbreak. To do so, they analyzed DNA from SARS-CoV-2 samples in nasal swab tests obtained from nearly 900 passengers and crew during the outbreak.

The genetic analysis suggests “that there was only one introduction of SARS-CoV-2, which spread among the ship’s passengers through possible mass gathering events in recreational areas,” according to the study.

The prevalence in coronavirus samples with a particular “cluster” of genes also suggests possible “over-diffusion” on board, long before quarantine began, the study authors said.

The virus may have spread silently at events as innocuous as a shared table or during “dancing, singing, shopping and watching performances,” the Kuroda group said.

While cruises may be a unique setting, the outbreak and quarantine aboard the Diamond princess reveals “how SARS-CoV-2 can spread in the community” more generally, the research team said.

Dr. Amesh Adalja is an infectious disease expert and lead scholar at the Johns Hopkins Center for Health Safety in Baltimore. Reading the new report, he said, “It illustrates how a contagious respiratory virus can spread widely from a single person in the right context.”

And for anyone still contemplating a cruise, the new findings show that “most cases may have been hired at mass gathering events on the ship, an important factor to consider as cruise lines begin to think about resume operations, “said Adalja.

The study was published on July 28 in the procedures of the National Academy of Sciences.

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