Aboard the Diamond Princess, a Case Study in Aerosol Transmission – The New York Times

Health

A computer model of the cruise-ship outbreak found that the virus spread most readily in microscopic droplets light enough to linger in the air.

The Diamond Princess cruise ship, docked in Yokohama, Japan, in February. More than 700 of the 3,711 people onboard tested positive for the coronavirus.Credit…Behrouz Mehri/Agence France-Presse — Getty Images

In a year of endless viral outbreaks, the details of the Diamond Princess tragedy seem like ancient history. On Jan. 20, one infected passenger boarded the cruise ship; a month later, more than 700 of the 3,711 passengers and crew members had tested positive, with many falling seriously ill. The invader moved as swiftly and invisibly as the perpetrators on Agatha Christie’s Orient Express, leaving doctors and health officials with only fragmentary evidence to sift through.

Ever since, scientists have tried to pin down exactly how the coronavirus spread throughout the ship. And for good reason: The Diamond Princess’ outbreak remains perhaps the most valuable case study available of coronavirus transmission — an experiment-in-a-bottle, rich in data, as well as a dark warning for what was to come in much of the world.

Now, researchers are beginning to use macroscopic tools — computer models, which have revealed patterns in the virus’s global spread — to clarify the much smaller-scale questions that currently dominate public discussions of safety: How, exactly, does the virus move through a community, a building or a small group of people? Which modes of transmission should concern us most, and how might we stop them?

In a new report, a research team based at Harvard and the Illinois Institute of Technology has tried to tease out the ways in which the virus passed from person to person in the staterooms, corridors and common areas of the Diamond Princess. It found that the virus spread most readily in microscopic droplets that were light enough to float in the air, for several minutes or much longer.

The new findings add to an escalating debate among doctors, scientists and health officials about the primary routes of coronavirus transmission. Earlier this month, after pressure from more than 200 scientists, the World Health Organization acknowledged that the virus could linger in the air indoors, potentially causing new infections. Previously, it had emphasized only large droplets, as from coughing, and infected surfaces as the primary drivers of transmission. Many clinicians and epidemiologists continue to argue that these routes are central to disease progression.

The new paper has been posted on a preprint server and submitted to a journal; it has not yet been peer-reviewed, but it was shown by Times reporters to nearly a dozen experts in aerosols and infectious disease. The new findings, if confirmed, would have major implications for making indoor spaces safer and choosing among a panoply of personal protective gear.

For example, ventilation systems that “turn over” or replace the air in a room or building as often as possible, preferably drawing on external air to do so, should make indoor spaces healthier. But good ventilation is not enough; the Diamond Princess was well ventilated and the air did not recirculate, the researchers noted. So wearing good-quality masks — standard surgical masks, or cloth masks with multiple layers rather than just one — will most likely be needed as well, even in well-ventilated spaces where people are keeping their distance.