Source

Seeing as many members of the SteemSTEM community just flew to and from Switzerland to visit the CERN laboratory, I thought I’d investigate a topic related to their travel. Specifically, I had always heard that it’s easy to catch an illness on an airplane because you’re enclosed in a tight space with hundreds of other people and have to breathe recirculated air for hours on end. I’ve assumed this to be the case for a long time because it seems like common sense. If one person on a plan is infected with an airborne pathogen, they should be able to infect others fairly easily. However, I’ve never actually seen studies that show this to be the case so I decided to look into this and determine whether it was a fact or an old wives tale.

Is the air safe to breathe?

I first looked into air quality on a typical airplane cabin because every time I hear the words “recirculated air” I get a chill down my spine. The term makes it seem like we’re breathing in the air exhaled by the other passengers along with all the other pathogens they’re infected with. Every time I turn on the little fan above my seat I worry a little bit about what exactly is flowing directly onto my face. Even the smell, while not outright offensive, can be a bit off-putting at times.

Fortunately, all available studies suggest that air quality in cabins is relatively good. The air itself is a combination of fresh air from outside and recirculated air. The fresh air is assumed to be completely sterile when the plane is at a high altitude and all recirculated air is passed through HEPA filters before reentering the cabin. HEPA filters have been shown to remove 99.97% of all particles and are fine enough to remove viruses (1). Thus, passengers can be relatively assured that the air being pumped into the cabin is sterile.

In 2002, a fairly robust study helped confirm that recirculated air was perfectly safe (2). A group of scientists polled over 1,000 passengers flying in planes that pumped either 100% fresh air onto passengers or 50% fresh and 50% recirculated air. The two types of planes were very similar otherwise and flight paths were always between California and Colorado. This study was naturally double blind as passengers are never typically informed whether or not their cabin is filled with recirculated air. After the extensive polling, the scientists concluded that the use of recirculated air on an airplane did not change the probability of a passenger experiencing illness.

Airflow in cabins is also designed to minimize disease transmission as well. In most commercial airplanes, air is pumped in above passengers and sucked out below them. This unidirectional flow of air ensures that any airborne pathogens shed by passengers are quickly removed from the cabin. The direction of flow also minimizes the amount of air transmitted across the length of the cabin. This minimizes the chance of direct air transmission between passengers in different rows. Although it’s difficult to determine exactly how effective air flow is at minimizing disease transmission, there are cases of severe outbreaks in non-ventilated aircraft showing how bad things can be without such airflow. In one instance, influenza was spread to 72% of passengers aboard a grounded plane without an operational ventilation system (3).

Outbreaks in the skies

Even though cabin airflow minimizes disease transmission, outbreaks have been known to occur on aircraft. The total number of verified outbreaks is small, and is limited to a few key infectious agents:

Tuberculosis:

Tuberculosis, a respiratory disease caused by an airborne bacterium of the same name, has caused the most concern among airlines companies and health organizations. This is primarily because it is one of the most widespread diseases on earth with almost a third of the world’s population thought to be infected (4). Many studies have investigated possible outbreaks and developed guidelines for minimizing disease transmission (5). Although tuberculosis is responsible for the majority of confirmed outbreaks on planes, a recent investigation only found 21 cases in which any evidence of tuberculosis symptoms were found (6). Still, the transmission of potentially antibiotic resistant strains of TB internationally remains a concern which explains why many countries either screen for TB or require vaccinations against it for immigrants or visitors.

SARS:

Public concern over SARS (severe acute respiratory syndrome) outbreaks on planes is primarily due to a few incidents that occurred between 2002 and 2003. This is, not coincidentally, right around the time everyone was panicking about SARS. One particularly well-documented event showed the spread of this disease from a “patient zero” to a number of nearby passengers (7).

Analysis of a SARS outbreak on a commercial airline. Adapted from (1).

As befitting an airborne illness, passengers closest to the index patient as they call him (I still prefer the term “Patient Zero”) were more likely to get sick. None of the passengers farthest away showed any SARS symptoms.

Norovirus:

Outbreaks or suspected outbreaks of Norovirus on a flight occur once every few years. This agent causes severe diarrhea, vomiting, and stomach pain and is a bit unusual compared to other infections agents in that it’s not transmitted by air (8). It’s still highly contagious when spread through food or water and that’s probably the still the cause with modern airline outbreaks. In one case, 59% of 379 passengers were infected with norovirus by contaminated flight attendants (9). Or possibly it was a disgruntled flight attendant that spit in everyone’s coffee…

Minimizing infection while traveling

Even though verified outbreaks are rare and air quality is fine, several studies have acknowledged that flyers are still at an increased risk of contracting a communicable disease (10). However, the factors associated with this increased risk apply to all forms of travel rather than being specific to airline transit. Heightened stress and disrupted circadian rhythms inhibit the body’s immune system and close proximity to other people as well a common use items like seats, trays, and toilets further increase the chance of infection.

With this in mind, travelers can take a number of steps to minimize their chances of getting sick (11):

Wash your hands This is especially important before any meals and after using any public facilities. Hand sanitizers like Purell are fine, but soap and water work just as well.

Keep the air vent open As I said before, the air pumped into the cabin is perfectly safe and having it constantly flow around you will remove nearby pathogens. It essentially functions as a laminar hood.

Hydrate and stay well rested This will improve overall health which will keep your immune system functioning normally.

If you wanted to go extreme, you could hole yourself up in a window seat in the back of the plane, wear a surgical mask, and never open up the tray. However, if you follow the above guidelines you should be fine.

The duration of flight is also a major factor on disease transmission. Most studies tend to agree that the risk of transmission of infection is minimal on short flights and much higher on flights over 8 hours in duration (11). You usually can’t avoid long flights, you might want to prepare more for them.

Safe travels

On behalf of TKing airlines, I hope you enjoyed reading this post. Before you depart, please place your vote in the full upright position and don’t forget to leave your comments below.

Images

All images used have been are taken directly from the publication referenced or from the movie Airplane. If any image owner has an issue with this article, please contact me and I will address the issue.

Sources

(1) https://www.ncbi.nlm.nih.gov/pubmed/15767002
(2) https://jamanetwork.com/journals/jama/fullarticle/195131
(3) https://www.ncbi.nlm.nih.gov/pubmed/463858
(4) http://www.who.int/mediacentre/factsheets/fs104/en/
(5) http://www.travelmedicinejournal.com/article/S1477-8939(07)00134-2/fulltext
(6) https://www.e-sciencecentral.org/articles/?scid=SC000015595
(7) http://www.nejm.org/doi/full/10.1056/NEJMoa031349
(8) https://academic.oup.com/cid/article/53/6/515/357038
(9) https://academic.oup.com/jtm/article/16/5/349/1817461
(10) http://www.businessinsider.com/why-airplanes-make-you-sick-2017-10
(11) https://www.huffingtonpost.com/2014/06/06/how-not-to-get-sick-on-planes_n_5367084.html
(12) https://books.google.com/books?hl=en&lr=&id=nc5Qq56_wQIC

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