Was Emirates Dubai-New York flight a bout of mass hysteria?
Many of us will have wondered what germs we are breathing in while sitting on board an aircraft.
Hundreds of passengers wedged in their seats for hours on end and breathing the same air might seem ideal for the spread of infection.
Certainly the blaze of publicity surrounding a recent Emirates flight from Dubai to New York highlighted concerns that passengers might have, whether these are justified by the evidence or not.
Reports in the United States indicated that as many as 106 people on flight EK203 complained of symptoms such as coughing and fever when the Airbus A380 touched down at John F Kennedy Airport on Wednesday morning local time.
Emirates said that three passengers and seven crew were taken to hospital for tests. Authorities subsequently confirmed that those hospitalised tested positive for influenza, or the common cold, but nothing more serious.
Influenza incubation period
Doctors can be sure of one thing: anyone ill with flu on arrival in New York would have contracted the virus before walking on board the aircraft in the UAE.
This is because the incubation period – the time between exposure to an infection and symptoms developing – is much longer than the 14 hours or so that a Dubai-to-New York flight takes.
“It's got to take a couple of days minimum and usually more,” said Peter Openshaw, a professor of experimental medicine at Imperial College London who, from 2006 to 2015, was a member of the UK Department of Health's Scientific Pandemic Influenza panel.
This raises the question of why so many individuals on the flight may have felt ill.
What Prof Openshaw described as a “mass hysteria” can cause large numbers of people to perceive that they are unwell, even if they are actually fine.
Yet it is the case that pathogens such as the influenza virus can spread between people on aircraft.
“There's evidence of transmission, particularly near the toilet because everyone goes to the toilet and may be leaving infected material on door handles. It's not impossible for outbreaks to happen as a result,” said Prof Openshaw.
There are several ways in which the influenza virus can spread on aircraft. For example, particles in the air can be breathed in. Material on door handles can infect a person if they go on to rub their nose or eyes.
When it comes to breathing in infectious particles, the risks are likely to be lower than we might imagine.
Who is at risk of infection on a plane?
Professor John Oxford, co-author of the textbook Human Virology and an emeritus professor of virology at the University of London, said filtering systems mean that air on board tends to be clean.
Passenger planes typically are fitted with High Efficiency Particulate Air (HEPA) filters, which are the same type of filters as are found in many home air-purifiers. Recirculated air is also mixed with air from outside.
Emirates flight 203
“A lot of infective bacteria and viruses are filtered out. Your best chance of getting infected is not on the flight, but queuing up, by getting in a taxi,” said Prof Oxford.
The key risk, he said, is to those sitting next to or within a few feet of an infectious individual.
Results released by scientists from Emory University in the United States tie in with this. Their findings indicated that the likelihood of transmission to those further away was “low”.
Infectious crew members, because of the number of passengers they interact with, may infect multiple individuals. The Emory University researchers found that an ill crew member is likely to infect an average of 4.6 passengers.
People seated next to a window are at lower risk of infection than those in middle or aisle seats.
When inflight air-conditioning breaks
There have been “extremely unusual” cases, Prof Oxford said, where the air-conditioning system breaks down and large-scale infections have resulted, but there is no evidence that this was the case with the Emirates flight.
One much-discussed instance of influenza transmission happened in 1977, when an Alaska Airlines Boeing 737 suffered an engine failure when attempting to take off, and subsequently sat on the tarmac for three hours. Although the air-conditioning system was broken, most of the 54 people onboard remained in the aircraft.
As a scientific paper in the American Journal of Epidemiology noted, within three days almost three-quarters of passengers developed symptoms such as coughing, fever, headache, sore throat, muscle pain and fatigue – all, reports indicated, from a single infected passenger.
Also, there have been cases where other infections such as severe acute respiratory syndrome (Sars) and swine flu, caused by the H1N1 virus, have spread on board an aircraft.
Although there have been numerous studies of the risk of onboard infections, further research and improved reporting of cases is needed to better understand the risks, Katrin Leitmeyer and Cornelia Adlhoch, from the European Centre for Disease Prevention and Control, concluded in a 2016 paper in the journal Epidemiology.
“There is evidence that influenza transmission aboard aircraft occurs, but the published data do not permit any conclusive assessment of the likelihood and extent,” they wrote.
How to avoid catching a cold on a plane
Those concerned about what pathogens they might be exposed to can reduce the risks. Keeping the overhead air vent open is one measure, as it leads to greater throughput of clean air. Not rubbing the eyes or nose is also advised.
Individuals at particular risk of serious illness when exposed to influenza, such as people with asthma, chronic bronchitis or diabetes, might, said Prof Openshaw, consider taking preventative drugs. Oseltamivir, sold under the brand name Tamiflu, can prevent flu.
“That's been demonstrated to prevent infection if taken by contacts with people [infected] by influenza,” said Professor Openshaw.
Read more: An A to Z of travel health
To reduce the likelihood of infecting those nearby, ill passengers may choose to keep their overhead air vent open to blow infectious particles towards the floor. Wearing a face mask can also reduce the chance of infecting others.
It is perhaps worth remembering, though, that the global media coverage that the Emirates flight attracted was not the result of multiple onboard infections.
“It's just bad luck it got a lot of publicity,” said Prof Oxford.