The crisis aboard the quarantined Diamond Princess cruise ship in Japan shows how germs can spread rapidly through air conditioning systems that can't filter out particles as small as the new coronavirus, one air quality expert says.
The quarantine ended last Wednesday, but not before the number of coronavirus cases reached 690 and three deaths were reported, according to the Associated Press.
By Tuesday, 36 American passengers of the hundreds evacuated from the Diamond Princess and quarantined in the US have so far tested positive for the virus.
Typical conditions onboard cruise ships probably contributed to those case numbers, one expert said.
"It's standard practice for the air conditioning systems of cruise ships to mix outside air with inside air to save energy," Qingyan Chen, a professor of mechanical engineering at Purdue University in West Lafayette, Indiana, explained.
"The problem is that these systems can't filter out particles smaller than 5 000 nanometers. If the coronavirus is about the same size as SARS [severe acute respiratory syndrome], which is 120 nanometers in diameter, then the air conditioning system would be carrying the virus to every cabin," Chen said in a university news release.
"Cruise ships could minimize this problem by just using outside air and not recirculating it," he added.
Chen studies the spread of, and ways to track, air particles in passenger craft. His team has created models to show how the H1N1-A flu virus and other pathogens move through aircraft cabins, and his lab's discoveries about the airborne nature of SARS could improve understanding of how the new coronavirus spreads.
On passenger planes, the new coronavirus is more likely to spread by touch than through the air, because the air conditioning systems of planes can filter out particles as small as viruses, Chen said.
However, airborne transmission of the virus can occur between people sitting in the same or neighboring row as an infected passenger.
"The further away you're sitting from a person who is infected, the better," Chen said.
Toilets would be the main source of coronavirus transmission on commercial flights.
"Stool also contains viruses. Close the lid before you flush to limit how much goes into the air. Planes should provide wet wipes with alcohol to prevent the spread of the virus through touch," Chen said.