Francesca Tomasi received her B.A. from the University of Chicago and is now a microbiologist.
It happens more often than you’d like: you’ve settled down in your seat and fastened your seatbelt, ready to take off for a long flight, and the person sitting next to you lets out a hacking cough. Just your luck. You spend the majority of your flight actively trying to face the other way and hoping you aren’t being exposed to something that will ruin your vacation or business trip. Maybe you feel stuffy a few days later and silently curse your seat buddy, but way more often than not you feel better within a week and move on with your life.
In a world where air travel can connect almost any two points on the globe in 24 hours or less, a little germ can travel a long way, settling its progeny on many people along its journey. One great way to spread germs? Coughing: it aerosolizes microbes to be inhaled by the next person to walk by, in addition to letting them settle on any other surface they happen upon. A few months ago, the WHO released its annual Global Tuberculosis Report, which concluded amongst other things that tuberculosis has re-emerged as a leading killer in the world, topping the list as the number 1 infective cause of death. One of the tell-tale signs of tuberculosis? A cough.
The European Center for Disease Prevention and Control (ECDC) recently published a systematic review on tuberculosis transmission on aircraft – after all, inhaling Mycobacterium tuberculosis is myriads worse than a bout of the flu, and therefore warrants a look at the actual risk of such spread. The authors of the study performed a literature search to identify cases of tuberculosis that were acquired by unlucky flight passengers. Out of 21 records that they found on the subject, 7 presented weak evidence of potential in-flight transmission. Only one of these cases was substantially supported as an aircraft-acquired infection. The authors conclude that the overall risk of tuberculosis transmission on airplanes is very low. Based on the evidence they gathered, which has its own limitations (tuberculosis diagnoses are difficult to make and often overlooked especially in poorer countries, which have significant air traffic), the authors estimate that “0.1 to 1.3% of aircraft contacts in long-haul flights (> eight hours) might have contracted the infection from a sputum-smear-positive index case. The risk of infection seems to be the highest among passengers seated within two rows of the index case.” Despite the low quality of evidence to support aircraft-acquired TB (or because of it), the authors end their paper by saying that “the risk of TB transmission on aircraft seems to be low…[they] concluded that this is not a research gap that should be prioritized and TB research resources are better directed elsewhere.” There you have it.
Regardless, airplanes can feel stuffy, especially during long flights, and you can’t help but wonder if this is true about any infectious disease lurking nearby. You sit shoulder to shoulder with up to several hundred other people, and statistics tell us that at least a small percentage of them are harboring some sort of illness like a cold or the flu. I come bearing good news: airplane air is actually quite clean, especially compared to other mass transportation vehicles like buses, where disease transmission has been shown to be a much more significant issue. On average, plane cabin air is refreshed twenty times an hour, which is once every three minutes. That’s more than most office buildings, which completely refresh once every 5 minutes. Furthermore, HEPA filters, the ones used in hospitals, are used for air circulation on larger airplanes. HEPAs remove about 99.97% of bacteria and any other airborne particles that viruses could latch on to. Finally, cabins are separated into distinct ventilation sections, which span about 7 rows of seats. This means that you really only share your air with your immediate neighbors.
Chances are that unless the person sitting next to you is hacking up a lung, you will not contract a respiratory illness as a result of the air circulation on a plane. You should, however, take care to wash your hands as often as possible, especially after touching surfaces such as tray tables, restroom doors, and overhead bin latches, all of which are indubitably loaded with viruses and bacteria. And that icky feeling you get after a long flight that you’ve been blaming on the sick guy sitting six rows behind you? It’s actually much more likely a result of the dryness and oxygen-thin composition of the air, which aircraft manufacturers have been working to improve.