Photo: Philip Fong / AFP / Getty Images
A new unpublished study of data collected during the COVID-19 epidemic on the Diamond Princess cruise ship in February suggests that the virus has probably spread through the ship’s air conditioning system.
The analysis, which has not been peer reviewed, was distributed by the health prepress server MedRxiv on Thursday.
Researchers at the British University of Bournemouth and King’s College London examined the rates of symptomatic quarantine infection in cabins with previous confirmed cases and compared them to those in cabins without previous confirmed cases, including including those in single occupancy rooms.
It was expected that the infection rate would be significantly higher in the cabins where cases were confirmed (passengers who tested positive and who were isolated from the ship). But the results showed that it was not.
The scientists concluded that the aerial transmission of COVID-19 via the ship’s ventilation system could explain how the virus spread in the cabins.
By February 20, 619 positive cases of COVID-19 – of which 301 were symptomatic – had been confirmed on the vessel. A total of 163 of them, 115 passengers and 48 crew members, recorded the onset of symptoms during the quarantine period from February 6 to 17. The analysis showed that 20% of these 115 passenger cases occurred in cabins where a passenger with a confirmed and symptomatic COVID-19 infection had stayed there. Eighty percent were in cabins that had no previously confirmed cases.
“It is not possible to deduce exactly when all the cases on Diamond Princess became infected due to the variance of COVID-19 incubation periods between individuals and the lack of presentation of symptoms in many cases “Wrote the authors of the study, Orouba Almilaji and Peter W. Thomas. wrote. “However, we assume that … the risk of infection is higher when there is close contact with a sick person in a small space such as the cabins of ships.”
The study found that the age distribution between cabins did not seem to make any difference in the results.
The role of ventilation systems in facilitating COVID-19 infections is increasingly monitored as the pandemic spreads. In a restaurant in Guangzhou, China, an epidemic involving three family groups in late January and early February was linked to the airflow from the establishment’s air conditioning system.
Another study has confirmed that speech droplets can persist in the air for tens of minutes. Droplets of infected individuals could transmit the disease in confined spaces and through ventilation systems.
The Diamond Princess HVAC (heating, ventilation and air conditioning) system is similar to that found in many restaurants, hospitals, nursing homes, gymnasiums, buses and trains, office buildings, prisons and schools.
The vessel does not have a higher ventilation rate or high efficiency air filters (HEPA) which effectively reduce the transmission of pathogens by air in aircraft.
“The design of the Diamond Princess air conditioning system shows that the air in the various passenger cabins has come together in one
air duct, mixed with a little fresh air (only 30%), then [was] replenished the various cabins, ”wrote the authors of the study.
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Mike Moffitt is an SFGATE journalist. Email: [email protected] Twitter: @Mike_at_SFGate