“Snakes on a Plane” was an intriguing movie title. “Microbes on a Plane” sounds more realistic and raises a common fear of colds, flu or worse. Here on “Today’s Woman”, our medical contributor, Dr. Judith Reichman, will help us understand if and why we are at risk for infections as we join the over one billion passengers who travel by air every year. Dr. Reichman answers some common questions:
Why do those who fly frequently complain of headache, fatigue, fever or breathing problems?
Some of these symptoms may be due to the low barometric pressure, oxygen content and humidity in the air cabin. When combined with jet lag, sleep deprivation, stress, (security concerns, long lines, missed flights, delayed and cancelled flights), as well as cramped seating, motion sickness and discomfort from vibration and engine noise, we have ample reason to feel “ill.” And let’s not forget that engine fumes can, on occasion, seep into the cabin.
While acknowledging all these factors, we also should consider whether infections can occur as a result of air water or food contamination and whether there is a risk of “catching something” from other passengers in the confined environment on the aircraft.
Is the closed environment of an airplane a repository for germs?
Not necessarily. In order to address the “is a plane a moving culture for viruses and bacteria” question, we have to understand how the aircraft cabin is ventilated. Once in flight, the air from the outside (which should be sterile at higher altitudes) is vented through the engines where it is heated, compressed and subsequently cooled. It then flows into the plane from overhead air vents, circulates across the aircraft and exits from the floor of the cabin. The airflow is laminar, i.e. side-to-side. This means it flows from top to bottom in lateral sections, not from front to back. Usually about 50% of the air is re-circulated, and as this happens, it passes through very special air filters, which remove dust, vapors, bacteria, and mold. Although a virus would be too small to be trapped by the filter, we know that viruses are usually attached (or spread by) droplets. And these are removed by the filters.
The air is usually exchanged at a rate of 15 to 20 air changes per hour, (compared to 12 air changes per hour in a typical office building). As a matter of fact, in a recent report to the House Subcommittee on Aviation, experts stated that “data from epidemiologic studies and microbiologic assays indicate that the risk of airborne infections currently appears to be very low.” And an independent published research showed that the concentration of biological microorganisms in planes is lower than in an office building, an ordinary city street and on public buses or trains.
So is there an infection risk for passengers?
Even if the air is appropriately circulated there are however, ways that infections can be transmitted to passengers:
- Contact infection. This occurs from body-to-body contact or from large droplets that are sprayed several feet when an infected person sneezes, coughs or talks. The virus or bacteria sprayed at you then enters your body and infects you through your eyes, nose or mouth.
- Airborne infection. This occurs when larger infected droplets partially evaporate. The residue or smaller droplets becomes widely dispersed in the air and remains there until the air is exchanged or appropriately filtered.
- Vehicle transmission. The microorganism is spread through infected food and water.
- Vector-borne transmission. Diseases (such as malaria) are spread through insect bites and vermin.
- The first two modes of transmission will account for the greatest risk of infection. That risk, however, is dependent on how infectious the “sick” person is, the proximity of his seat, and duration of the exposure. (Flights over eight hours appear to be of greatest risk).
Which diseases are most likely transmitted through cabin air?
- The common cold. Believe it or not, there are very few published reports of cold outbreaks as a result of air travel. That may be due to the fact that colds are so common that it’s difficult to compute whether they were “caught” on a plane. Also the decrease in the humidity of airplane air with subsequent drying of nasal passages, fatigue and proximity to someone who is sneezing and coughing are variables that affect a person’s susceptibility and the likelihood of infection with cold viruses. But “infected” plane air is probably not to blame; a study of the percentage of fresh air, which was re-circulated in the cabin (50 percent versus 100 percent), showed that it made no difference in the development of upper respiratory tract infections. (This would not be the case, however, if the plane is on the ground, the doors are closed and the air system is shut off.)
- Influenza. We know that air travel allows individuals from one area of the world to spread a specific type of flu to another and indeed, air travel is probably the chief cause of global spread. But there is less concern about actual in-flight transmission, unless the aircraft is grounded with an inadequate ventilation system. In that case, there have been documented outbreaks. The current recommendations require “that passengers be removed from an aircraft within thirty minutes of shutting off the ventilation system”. As the new flu season approaches, the best way to decrease your chances of infection is to get your flu shot, and remember, immunity occurs two weeks after the vaccine, so plan ahead.
Other airborne diseases:
- Meningitis. This can be spread by contact with respiratory secretions. There were 21 reports of suspected travel associated meningitis cases that occurred between 1991 and 2001. It was felt that these were contracted as a result of close proximity of passengers to an onboard contagious individual.
- Measles. This too is very contagious and the latest known airborne infection occurred in 2002 when children from an orphanage in China were brought to the US and apparently were contagious at the time of their flight.
Other airborne “large droplet” diseases include:
- Tuberculosis. This disease is global; one-third of the world’s population is currently infected. Studies since the mid-1990’s have documented in-flight TB transmission. The largest USA incident occurred when a passenger traveling on a trip from Baltimore to Honolulu affected four of fifteen passengers seated within the closest two rows (they didn’t all develop TB, but they did have positive TB skin tests). A risk analysis published in 2004 estimated that the overall probability of TB infection during a long air flight is around one in a thousand, when a person with TB symptoms is on the plane. This is similar or perhaps even less than the chance of becoming infected by a person with TB in other confined spaces.
- SARS. This is transmitted by large airborne droplets or by direct contact. There has been substantial evidence that in 2003 during the SARS outbreak, transmission of the virus occurred through airplane air to passengers seated within five rows of the initially infected person and that the infection occurred on fairly short flights. (In one three-hour flight from Hong Kong to Beijing 22 of 120 passengers contracted SARS). Since then, the “epidemic” has dissipated and there have been no major outbreaks of concern.
What about food and water contamination?
Microorganisms that cause food poisoning and gastroenteritis diseases usually are spread by contamination of food or water. These include salmonella, staphylococcus, cholera and a virus called Norwalk-like agent. No food borne or water borne outbreaks have been reported over the past few years, probably because the food is so often pre-packaged and frozen.
The water in on-flight tanks, especially if filled from water sources which are less than “pure” may be contaminated. Long or repeated storage within the tank can, despite best efforts, result in bacterial growth. If you don’t want to drink the water in the country from whence the flight originated, don’t drink the water from the plane tank. Bottled water is always the safest way to maintain hydration.
Vector (mosquito) borne diseases:
- Dengue fever
- Yellow fever
Mosquitoes that carry these diseases can be imported by air. Depending on the carrier and the country that the plane is coming from or going to, a disinfectant may be sprayed into the cabin. The U.S. stopped the practice of spraying while passengers are on board because this too can cause reactions and breathing problems.
What about the dry air?
The humidity within the cabin is usually below 25 percent can definitely cause sinus and mucous membrane discomfort. We would probably feel better if the humidity was 35% (that’s what it is in a comfortable home environment), but increasing humidity can also encourage growth of bacteria and fungi, especially in the aircraft water tanks; hence the airline industry has hesitated to do so.
So what can we do to stay healthy when we fly?
- Respect others. Don’t fly if you are sick. Aside from concern for the other passengers’ health, flying with an ear, nose or sinus infection and/or severe congestion, may cause obstruction of airflow in your middle ear and sinuses during takeoff and landing. This in turn can cause severe ear and sinus pain and injury to the eardrum.
- Prevent dehydration. Drink plenty of water (and make sure your children do this, they are especially susceptible to dehydration.) If you want to ensure that the water you drink is not contaminated, ask for bottled water. Don’t add ice cubes if they are made from water that could be unsafe. Drink tea and coffee only if the water used to make it is boiled or is bottled.
- Limit caffeine and alcohol, these add to dehydration and jet lag.
- Prevent dryness of your skin, eyes and airways. Use moisturizer, saline eye drops (or rewetting drops) for contact lenses and saline nasal sprays. (As I write this I’m aware of the restrictions on bringing these items on board the plane; I hope they will be reversed. You can always get a note form your doctor for the eye and nose drops.)
- Practice good hand hygiene. Wash your hands before you eat. Don’t put your unwashed hands in your mouth or rub your eyes.
- Move. If someone nearby seems sick, ask if you can move to another seat. And don’t forget, even if you are surrounded by healthy individuals, it’s important to get up, move and stretch to prevent blood clots and deep veined thrombosis (DVT).
- Mask? The use of masks to prevent infection within the aircraft carrier is unproven.
Dr. Judith Reichman’s Bottom Line: Work, recreation and families have become global. Most of us have to fly. With rare exceptions, we don’t risk serious illness. Simple hygiene, hydration and judgment can help prevent air related health problems.
Dr. Judith Reichman, the “Today” show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," which is now available in paperback. It is published by William Morrow, a division of HarperCollins.
PLEASE NOTE: The information in this column should not be construed as providing specific medical advice, but rather to offer readers information to better understand their lives and health. It is not intended to provide an alternative to professional treatment or to replace the services of a physician.
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