H1N1 flu infections are more easily spread during plane travel, researchers at University of California, Los Angeles (UCLA) have predicted.
Dr. Sally Blower, along with Bradley Wagner and Brian Coburn, used novel mathematical modelling techniques to predict in-flight transmission of the H1N1 virus.
They found that transmission could be rather significant, particularly during long flights, if the infected individual travels in economy class.
Specifically, two to five infections could occur during a five-hour flight, five to 10 during an 11-hour flight, and seven to 17 during a 17-hour flight.
"Clearly, it was air travel, by transporting infectious individuals from the epicenter in Mexico to other geographic locations, that significantly affected the spread of H1N1 during the outbreak last spring. However, until our study, it hadn't been determined how important in-flight transmission could be. Therefore, we decided to make a mathematical model and predict what could be expected to occur during a flight," said Coburn.
The researchers used methods from the field of quantitative microbial risk assessment, and determined the number of potential infections in one transatlantic flight, assuming there was just a single infected passenger on board.
Specifically, they used the long-established Wells-Riley equation, which is based on the number of exposed individuals, the respiratory rate of the infected person, the length of exposure to the infectious droplets and the concentration of infectious viral particles over time.
Within an aircraft, the concentration of particles over time is determined via ventilation rates, the volume of the cabins in the aircraft and how sick the infected person is.
"Importantly, we found that the number of infections that would occur on a flight was very dependent on which cabin the infected individual was sitting in. We found that many infections could occur if the infected individual was travelling in economy class but relatively few if the individual was travelling in first class," said Blower.
The researchers tried to find out why more infections occur in economy class.
"Primarily, it's the more crowded conditions in economy. And unfortunately, there is a very high probability - 75 percent - that if an infected person is on board, they will be in the economy cabin," said Coburn.
The researchers noted that their results have important implications for understanding and predicting the global dissemination of H1N1, suggesting that air-travel restrictions may be useful in controlling influenza pandemics.
"Our results imply that one individual travelling by plane, by infecting other travelers on the same flight, could cause multiple simultaneous outbreaks in different geographic locations rather than causing only one outbreak. For that reason, quarantining passengers who travel in economy class on long-haul flights could potentially be an important control strategy this winter, but there is no point quarantining passengers in first class," said Wagner.
The study has been published in the current online edition of the journal BMC Medicine.