Infectious disease spread on airplanes

A recent post of mine seemed to briefly address the issue of the spread of infectious disease during air travel, without giving too much “meat” behind it. I thought there might be some interest in this subject and I would like to refer to an outstanding article, from the Lancet 2005; 365: 989-96, written by Mangili and Gendreau.

Clearly, the number of people who travel via air, is a staggering number with annual estimates well over 1,000,000,000 worldwide and over 600,000,000 in America, alone. Air travel is exciting and can be the most enjoyable part of the trip for some, but it also places one at risk for infectious disease.

The Cabin Environment

The spread of infection in commercial aircraft cabins is subject to several factors. The environment of the the cabin itself is perhaps the most important. The cabin, offering a pressurized environment and low humidity, requires that passengers and crew are in close proximity of each other. When parked, the fresh air is supplied via an auxilary power unit but during flight, fresh air is sent into the cabin from the engines where it is has been heated and compressed; outside air at typical cruising altitude is presumed to be sterile. Air enters the cabin from overhead, circulating downward and exiting from the floor. This is designed to help limit the spread of airborne particulate through the cabin.

Most commercial airliners use 50% re-circulated air for improved fuel performance and humidity control. This re-circulated air is filtered with a HEPA (high efficiency particulate air filter) system. Several studies have shown that standard cabin air is exchanged 15-20 times per hour compared to 12 per hour in a typical office. A survey demonstrated that most airlines use HEPA filters, although it is not a federal requirement.

How Disease is Spread

Before we look at specific diseases, transmission of disease should be understood. Mangili and Gendreau offer 4 “modes of disease transmission”: Contact, Aerosolized, Common Vechicle (food and water) and Vector. “Contact” is just what you’d think, direct contact with a person or their body fluids. This also includes direct contact with a contaminated intermediate host, like a fomite. Large droplets (>5 microns) also fall into this category and can be transmitted when a person coughs, talks and/or sneezes. These particles travel a short distance (less than 1 meter) and land on a mucous membrane like the eyes or nasal passages or fall quickly to land on a lower surface. Aerosolized droplets are considered <5 microns and can disperse widely, remaining suspended in the air for indefinite periods of time. Contact and Aerosolized are key transmission routes for airborne illnesses, such as TB, SARS and Influenza. Remember to stay hydrated, which will help keep those mucous membranes (nasal passages, lips and eyes) moist and not dried or cracked.

Disease Specifics

Tuberculosis is a major global health concern and subject of recent media attention related to travel. An excellent reference for learning about this can be found in the World Health Organization publication called: Tuberculosis and Air Travel: Guidelines for Prevention and Control. TB has offered the most information and is perhaps the most studied of all infectious disease on aircraft. Two of the seven studies, cited by Mangili et. al, demonstrated a probable link with onboard transmission. One specific study found the index (first) case to be a flight attendant and of the almost 300 exposures on the flights, there were only two documented skin test reactions. A second case study involved a passenger infected with TB who flew from Baltimore though Chicago to Hawaii. Four of fifteen passengers, all seated within 2 rows of the index case subsequently had positive TB skin tests. While the transmission of TB on an airliner is obvious, it is of interest that there has never been an active case of clinical tuberculosis acquired from air travel.

The association of influenza and airline travel extends far beyond the infection of passengers. Airlines are a major contributor towards the rapid migration of infected people throughout the world. Influenza can spread, with the assistance of commercial airline travel, around the globe in a few hours. One particular study of interest, was the case of Influenza A/Texas Strain outbreak on a commercial airliner in 1979. The authors of the paper found that 72% of the passengers were infected with influenza within 72 hours of flight. They went on to state that the most likely reason for this high attack rate was the 3 hour ground delay with a non-functioning ventilation system, during repair work. The passengers were kept on the plane the entire time.

SARS (sudden acute respiratory syndrome) has also contributed to the study of inflight disease transmission. This atypical pneumonia-like illness is caused by a virus. There are obvious connections with the spread of SARS and in-flight infections. The case of interest, featuring SARS spread within aircraft, is of a flight from Hong Kong to Bejing. This flight was only a 3 hour duration and there were passengers infected as far away as 5 rows infront and 7 rows behind the index case. Luckily, there have been no reported cases of SARS on-board transmission, since March 2003. This is largely due to the WHO guidelines on SARS containment aboard aircraft.

Meningitis and Measles also deserve to be mentioned. Measles caused a recent scare aboard a flight from San Diego to Hawaii and there were 21 suspected cases of air travel associated meningococcal disease from 1999-2001.

Let’s not forget the food-borne illnesses, such as those spread by the “fecal-oral” route. A very well-written article titled Hygienic Quality of Food Served on Aircraft presents a wealth of information on the topic. For example, a total of 41 food-borne outbreaks aboard aircraft were documented from 1941 to 1999. These outbreaks infected almost 4000 people and caused 7 deaths. There have even been several cases of Cholera transmission in-flight. Most cases involve cold food dishes served in-flight and prepared by local suppliers. Thankfully, the last 5 years have seen a decrease in food-related illnesses, likely due to more common use of frozen and pre-packaged meals.

Practical Help

The authors of “Transmission of infectious diseases during commercial air travel” have noted several factors that place one at risk for airline acquired infectious disease. First, as with real-estate, location is key. Sitting within 2 rows of an infected person for a duration of 8 hours is the key. Second, ventilation of the cabin has an obvious role. One air exchange of the cabin removes 63% of the airborne organisms. Remember there are normally 15-20 air exchanges per hour in a commercial aircraft, versus an office with 12. One investigation involving TB modeled that doubling the ventilation rate within the cabin decreased infection risk by half. Lastly, handwashing works.


As more specialties begin to collaborate, new methods of data gathering are becoming available. There is a lack of sufficient data at present for a meta-analysis (study method to infer disease risk) because many studies are limited by incomplete passenger manifests. In fact, one study found that contact information for passengers with a tuberculosis exposure was inaccurate 15% of the time, when health officials were attempting follow-up.

While this is in no means a comprehensive review, it has hopefully given a good survey of infectious control in commercial airlines and suggestions of further reading. As with anything, there is no subsititute for common sense and you should always consult with your personal health care provider for further details and individual needs.

Bacteria in aircraft a low risk to travelers

Science Daily released an interesting article, based on research conducted at University of Massachusetts Amherst, that shows the low risk of air travel and bacterial illness.

Bacteria that was present in aircraft — with exotic names like Psuedomonas, Bacillus and Staphylococcus — are commonly found on healthy skin and not generally causative organisms of disease.

The research team sampled the air from twelve aircraft (Boeing 767) cabins with flight times of 4.5 to 6.5 hours. The samples were taken from the coach section of the plane at 6 different intervals, including boarding, climb, cruise and deplaning. As expected, the highest concentrations of bacteria was found during boarding and deplaning. When the passengers move through the plane, their activity stirs up dust and skin bacteria, releasing it into the cabin air. During the flight, the bacteria levels decreased, likely due to a decrease in activity in the cabin.

Doc, I have malaria…why are you looking down there?

Medical News Today ran an interesting article covering the efficacy of rectally given anti-malarial medications. The purpose of using a suppository to deliver the medicine, Artemisinins, is a fairly new concept and can prove useful to prevent a life-threatening delay of intra-venous medications to combat severe forms of malaria.

The study looked at over 1000 patients and compared rectal administrations of several different medical compounds, all artemisinin derivatives. Interestingly, the article also compared these medicines with a standard treatment of quinine.

Ease of administration, portability and lack of special training for use are benefits of rectally administered medications. Delays in treatment of severe forms of malaria can result in death and travelers who are in remote locations and suffering from malaria might benefit from beginning this form of treatment, while seeking definitive medical care.

This might also serve as a reminder that the person trying to treat you for malaria in a remote area actually knows what they are doing when they are “checking down there”.

My Weekend in Azeroth

This last weekend, I had very little time off and was in bad need of a trip and a little adventure. Knowing that I had to work this weekend, I chose to take my “vacation” to Azeroth. My decision to visit there was a great choice and I had a weekend full of adventures, looted treasure, monsters and magic. I visited several continents around Azeroth and only died a few times.

For my trip, I booked a tour with Naturally Rebellious, a guild with a lot of experience touring “noobs” around both continents. I can say that my guides were very professional, gave great service and explanations as we went, including history of the areas. They even cooked for me, secured lodgings and taught me a few things to keep me out of trouble on the journey. In fact, they had to heal me after several close calls, including a severe bear mauling, outside Astranaar.

The tour started in the beautiful city of Darnassus, the capital of the Night Elves and probably the safest city on both continents. My guides met me at the Warrior’s Terrace and made sure I was properly equipped for adventures. I needed a sword, bow, armor, magical potions and some food.

Darnassus was a great city and very beautiful. Merchants and craftsmen have their shops built, alongside houses, right into the massive trees. It reminded me of the redwood forests in Northern California. There is even a large lake in the center, where I learned to fish. After a few tries, I was able to start dragging some Longjaw Mud Slappers to the shore. After a bit of preparation and the standard guide safety briefing, including waivers and something about “risk of death and if death does occur, Naturally Rebellious is required to resurrect said corpse within 5 minutes” we started. It was a little un-settling.

The trip out of Darnassus involved an animal called a Gryphon. This is basically a large flying bird, ridden like a horse. Surprisingly, they were kept in very good condition by their trainers and did not smell as bad as I expected. I learned this was to be our primary means of transport, for the tour. Darnassus is on an island, and there are boats to travel to the mainland, but the gryphon was a great way to get a “bird’s eye view” of the landscape and see the area. Next stop…the Continent of Kalimdor and the port city of Auberdine.

Auberdine was my first real chance to get some adventuring in and test out my newly acquired skills. We gathered some herbs and I learned to make some potions of my own. I was fighting with the bears for a bit and had a great time. I noticed I was quickly ushered out of the city by my guides and told it was “for my own protection”. Apparently, this is a favorite raiding area for the “bad guys” of the world, the vile Horde. True to form, the horde showed up and laid quite a massacre on the unprepared and those insane enough to join the fight. I would advise extreme caution in this town, due to political instability and civil unrest. Still, the town was nice and the clam chowder was superb.

Pushing on, we took the gryphons to the Barrens for a wildlife safari. Roaming around the vast, dusty plains allowed us to see some exciting animals, very up close and personal. Highlights included the Zhevra, a cross between a unicorn and a zebra and the Kodo, a very large and slow dinosaur type creature. We visited the Goblin city of Ratchet. A meal of bear steaks and blood sausage topped off the visit, before we headed down to the Shimmering Flats to watch a drag car race at Mirage Raceway. I even got an autograph and picture with the champion driver Nazz Steamboil!

Our next leg was one of the most exciting for me, because we got to take a long boat trip, from the port city of Ratchet, to the other continents of the Eastern Kindgoms. We docked in Booty Bay, a pirate and goblin town on the southern most part of the land. Fishing is the center of business in Booty Bay, unless you count piracy. After a hard day of fishing and fighting both buccaneers and angry gorillas, we stayed at the notorious Salty Sailor Tavern. This was my first experience with Junglevine Wine and we ate some very good Spotted Yellowtail and Rockscale Cod. I even entered the weekly fishing tournament and won a lucky fishing hat! If you make it by the Salty Sailor, tell Nixxrax Fillamug, the bartender, I sent you.

Our final stop was the human’s capital city, Stormwind. This is Azeroth’s version of New York City. Everything is here and you can learn or buy what ever you can imagine. The Trade District was bustling with people chatting, checking their mail, making trades, purchasing new gear and running from district to district, within the city. The statues lining the entrance to the city were majestic and I even enjoyed the smoky and noisy Dwarven District. No trip to Stormwind is complete without a trip to the Mage Quarter and the Wizard’s Sanctum that houses the Stormwind Academy of Arcan Sciences.

With great sadness, I knew this trip to Azeroth was over. I wasn’t too worried because I knew I would visit again, very soon. I made some great friends and killed a few Orcs at the same time. If this sounds like your type of fun, pick up a copy of World of Warcraft and take a trip you won’t soon forget. When was the last time you got to save a princess, overthrow an empire and catch some fish all in the same day? Now that is a vacation!

Getting High on Your Holiday

Sure, we’ve all thought about it and some of us do it often. Getting high on your holiday trip can be pretty fun, in fact. I mean really high, above 11,500 feet (3500 m). Not everything cool is on a beach at sea-level. Ruins in the Andes, trekking in the Himalayas and chasing back country powder are a few things you have to get high, to do. These trips are all “dream vacations,” so why risk a problem with altitude sickness?

High altitude is considered to be 1500 – 3500 m (4950 – 11,500 ft) while very high altitude covers 3500 to 5500 m (11,500-18,050 ft). Anything above 5500 m falls into the extreme altitude category. Altitude sickness is not related to physical fitness and can have some deadly consequences, if not recognized and treated promptly.

Accute Mountain Sickness generally includes symptoms of headache, worse at night or during straining, nausea/vomiting and dizziness. The symptoms are often described as a “bad hangover”.

Some conditions associated with more severe forms of altitude sickness or AMS (acute mountain sickness) include HACE (high altitude cerebral edema) and HAPE (high altitude pulmonary edema). These conditions involve swelling and fluid accumulation in the respective tissues. Swelling of the brain, as seen in HACE, can present as marked stupor and confusion. HAPE, with fluid collecting in the person’s lungs, often starts as a cough followed by progressive shortness of breath.

As with most things, prevention is better than treatment. Prevention of AMS and it’s associated conditions centers around a slow, gradual ascent to altitude. This gives the body a chance to acclimatize and adjust to the physiologic demands of life at the new altitude, even if only for a few hours or days. This can be a problem for people traveling by car or plane to an area of high altitude, simply because they ascend very rapidly.

Symptoms of AMS can begins quickly, in as little as 2-3 hours after arrival to altitude, which means you can get off your plane and begin to feel bad, even before you arrive at your hotel! In an ideal world, all travelers going to higher altitude will be able to have a slow and controlled ascent, gaining no more than 600-900 m (1,980 to 2,970 ft) per day. However, this is not always practical. Anytime there is suspicion of an altitude related illness, stop ascending, immediately. If symptoms do not improve, consider a descent to lower altitude, for a few days of further acclimatization. Some expedition physicians also believe that most all medial problems, at high altitude, are to be considered AMS until proven otherwise.

There are a few medications used to combat AMS and a few good arguments, both for and against their use. The medicine that is most commonly used is called Acetazolamide. This medicine causes an acidosis, designed to combat the alkalosis caused by hyperventilation at high altitudes. Designed to be taken a few days prior to ascent, during the time at altitude and for a few days after descent, Acetazolamide is both a prophylactic medicine as well as a treatment. There is some controversy over the ideal dose to be used and I consider this article a good source of information, along with an article that favors a higher dose.

Against Acetazolamide Use:

Everything in life is a trade off and medicine is a perfect example of this. Side effects of Acetazolamide include a metallic taste, especially with soda, and frequent urination. Acetazolamide is a sulfa-based drug and allergic reactions can occur. Some studies have show than judicious exercise, on the first few days of arrival to altitude, can be effective in AMS prevention and that only 25% of travelers to resort communities at 8,000 and 12,000 feet have altitude illnesses.

For Acetazolamide Use:

A dream vacation can be ruined by many things and with 25% of travelers in an high altitude zone experiencing AMS symptoms, why risk spending your trip with a headache, or worse. Most vacation trips to high altitude zones last 7-10 days and Acetazolamide is a cheap and very effective medication for control and prevention of AMS.

Some other treatments for AMS, HACE and HAPE include dexamethasone and inhaled asthma medications like salmeterol. For the hard-core out there, Gamow bags can be used, especially on mountaineering expeditions. Ginko Biloba is also currently showing promise in AMS treatment/prevention.

As with most travel-related illnesses, prior proper preparation prevents poor performance. Understanding altitude illness and being aware of it’s symptoms can help with early recognition and treatment, thus preventing a ruined trip and health risk. To learn more about AMS check out these sites:

The International Society for Mountain Medicine

The High Altitude Medicine Guide

CDC Traveler’s Health Yellow Book: Altitude Illness