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A new preprint* released today analyzed data from the Diamond Princess Cruise Ship suggesting that SARS-CoV-2, the coronavirus that causes COVID-19, does not travel in the air very far.
This is important because it reinforces the safety of going outside, enjoying sunshine, and taking walks, as long as we keep 3-6 feet distance from others and follow the other hygiene and social distancing recommendations.
Background
A passenger joined this ship on January 20, who came down with a fever on January 23 that was confirmed on February 1 to be COVID-19. The ship was quarantined at sea on the morning of February 5, and the passengers were quarantined to their staterooms until February 19. Most of the staterooms had a maximum occupancy of four passengers. On March 1, the passengers and crew left the ship.
By March 5, 552 out of 2666 (21%) of the passengers had become infected, and 144 out of 1045 (14%) of the crew had become infected.
The researchers used the known incubation period of the virus and the date of onset of each case as determined by the development of symptoms in order to estimate when the infections occurred.
The Virus Spread in Two Waves
Beginning on January 28, there was a small wave of spread occurring in people who shared a stateroom and a much larger wave of spread occurring in people who did not share a stateroom. The large wave was overwhelmingly dominant and ended on February 5, reflecting the implementation of the quarantine.
The large wave was associated with a reproduction number (R-naught) of eleven, which is much higher than anyone has suggested for the virus in general. This is the number of people that one infected person can spread it to. The high reproductive number can easily be explained by the fact that a cruise ship has lots of people in tight spaces with plenty of opportunities for mass gatherings at pools, casinos, theaters, and so on.
After the quarantine, a second wave of transmission occurred in passengers who shared a stateroom, and in the crew. No second wave occurred in passengers who did not share a room.
This can be explained as follows:
Those who shared a stateroom had close contact with each other. This would potentially include coughing or sneezing, touching, talking face-to-face, and transmission across surfaces from respiratory secretions or fecal matter.
The crew had to service the passengers and were in close contact with one another while working.
The Virus Did Not Spread Very Far in the Air
Many of the staterooms had access to the open air via balcony doors.
The air in the staterooms themselves was connected by central AC, through which 70% of the air in the staterooms was indoor air and 30% was fresh outdoor air. The industry standards for the AC system suggest that air traveled at a rate of 8 liters per second, similar to the standards for office space.
If the virus were released into the open air and capable of traveling significant distances, it should have been able to travel from one stateroom to another through the AC system, and perhaps through the fresh air around the ship that came in and out of the stateroom balcony doors. That this did not happen suggests that the virus does not travel very far in the air.
The Bottom Line
This study reinforces the importance of avoiding mass gatherings, on the one hand, but reinforces the safety of the open air on the other. Staying inside all day is stressful and will have its own health toll. Going out in the sunshine and fresh air has physiological and psychological benefits, and is safe as long as we follow the recommended hygiene and social distancing norms.
Stay safe,
Chris
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Disclaimer
I am not a medical doctor and this is not medical advice. I have a PhD in Nutritional Sciences and my expertise is in conducting and interpreting research related to my field. Please consult your physician before doing anything for prevention or treatment of COVID-19, and please seek the help of a physician immediately if you believe you may have COVID-19.
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*Footnotes
* The term “preprint” is often used in these updates. Preprints are studies destined for peer-reviewed journals that have yet to be peer-reviewed. Because COVID-19 is such a rapidly evolving disease and peer-review takes so long, most of the information circulating about the disease comes from preprints.