The risks of catching an infection from an ill passenger are not as high as you would think, says Christine Pearson, a spokesperson for the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. “It’s not any more dangerous than any place where you are in touch with lots of people – like a shopping mall food court for example.
John Oxford, a virologist at Queen Mary University, London, agrees. He points out that the aeroplane ventilation goes from the ground to the ceiling, where the air is filtered for bacteria and viruses before it recirculates. Simulations looking at the potential spread of germs have found that they are generally confined to just a couple of rows either side of the carrier. Even then, the chances appear to be small, according to a study published in the British Medical Journal. The paper looked at a flight involving nine school children who were later found to be carrying the swine flu virus. Just two other passengers, of more than 100 questioned, later developed the illness – and they were both sitting within two rows of the ill school kids. As a result, the researchers concluded that there was just a 3.5% risk of catching the illness if you were sitting in those seats. A handful of other studies, looking at measles and TB, also suggest that in-flight transmission rates are similarly low. From studies such as these, Oxford says that “the biggest risk is not on the plane, but in the taxi on the way to the airport”.
However, John Edmunds, professor of infectious disease modelling at the London School of Hygiene and Tropical Medicine, points out that it is difficult to come to any firm conclusions, even for the more prevalent diseases. The number of studies is small, he says, meaning you can’t find absolute figures for the risk and compare that to the risk of infection in a school, say. So it is even harder to assess the risk of in-flight transmission of rare and unstudied diseases like Ebola.
Mode of transmission is clearly a factor. There are a few documented cases of norovirus spreading among passengers – probably due to people sharing the same toilet. But we know that Ebola is relatively difficult to catch: unlike respiratory diseases like colds and flu, it can only be transmitted through contact with bodily fluids like saliva, vomit, or blood, which begins to secrete out of every orifice. Although it is unlikely that someone suffering the full-blown attack would attempt to fly, it is not impossible. Patrick Sawyer, a US citizen who died from the virus last week, showed some of these symptoms on a flight from Liberia to Nigeria, raising fears for the other passengers. Airline staff and public health officials should be more aware of the dangers now, however, and should place anyone suspected of having the disease in quarantine. “Everyone is on the lookout,” says Oxford.
There is always the chance that a passenger could board a flight before they have developed the full-blown symptoms. But so far, the evidence suggests you are unlikely to catch it from someone in the early stages of the disease, before they have started vomiting and bleeding. “I wouldn’t want to be a passenger next to a guy with Ebola,” admits Edmunds. “But if they are just sitting there with a fever, I can’t imagine the situation being high risk.” Oxford points out that basic hygiene measures should further reduce the chance of infection – even if it can’t eliminate the danger completely. “The Ebola virus is very easily killed; you can kill it with hot water and soap,” he says. “Alcohol rubs get rid of it in a microsecond.”
Edited from Ebola: How easily do germs spread on planes?.