Explained: Do airplanes put you at extra risk of catching disease germs?

Research has not provided conclusive evidence of airline passengers being at a greater risk of infection than people in other crowded places. (Getty Images)

Israel's Ministry of Health said last week that a 43-year-old flight attendant with the country's national airline was comatose with encephalitis after she contracted measles on a flight from New York City to Tel Aviv, and asked all passengers on board the flight to see a doctor if they developed a fever, or showed other symptoms such as a cough, a runny nose, or a dark red rash.

In February, an adult contagious with measles infected two fellow passengers on a flight to San Francisco from an Asian airport, California health officials said this month.

A large number of cases of measles this year in the United States - which eliminated the virus in 2000, but is currently in the middle of a major outbreak - have been linked to people who flew into the country on airplanes. A total 81 flights were investigated in 2018 for carrying at least one infected person, up from 15 in 2017 and 10 in 2016.

Does flying increase the risk of contracting a communicable disease?

In general, according to the WHO, research shows "there is very little risk of any communicable disease being transmitted on board an aircraft". The quality of the air in the cabin is carefully controlled: ventilation rates provide a total change of air 20-30 times per hour, and recirculation systems recycle up to 50% of the air, with recirculated air being passed through filters similar to the ones used in hospital operating theatres and intensive care units. Also, the risk of infection from a passenger seated in the same area of the plane isn't any more compared to the risk in a train, bus, or other crowded places. During the SARS outbreak of 2003, the risk of transmission of the disease in aircraft was found to be very low, says the WHO.

That said, measles is among the world's most contagious viruses. Unlike influenza pathogens, which spread with sneezes or coughs, the measles virus hangs in air like dust for up to two hours. Also, as a report in The New York Times pointed out, while a person with influenza was likely to infect two unimmunised others, one infected with measles could give the disease to up to 19 inpiduals who had not received the measles, mumps, rubella (MMR) vaccine.

In general, the unimmunised, the very young, and those with weakened immune systems due to cancer or other serious diseases, are more vulnerable. Exactly where in the aircraft you sit in relation to an infected person also matters greatly, research published in the Proceedings of the National Academy of Sciences (PANS) of the United States of America in April 2018 showed.

According to the researchers, passengers seated one row in front, one row behind, or two seats of either side of an infected flier were within the "perimeter of risk"; those sitting farther away were much safer. Which underlined that the risk came from proximity to an infected person, and not from being on an aircraft per se with them. "Modern aircraft are becoming increasingly better about their air circulation, and it's changed actually much more frequently now than your average office building," lead researcher Vicki Stover Hertzberg was quoted as saying in media reports on the study.