I have just returned from Israel. Ten time zones and a 15 hour (if it’s non-stop) flight will guarantee jet lag. So please forgive me if this piece is somewhat disjointed. The El Al flights I took were uneventful and indeed I slept most of the way. But as I landed in LA my ear painfully popped, I started coughing and sneezing, had a sore throat and generally felt awful.  I was reminded of a segment that I had done for the Today Show titled “Microbes on a Plane”. (It was supposed to be a take-off on that awful movie “Snakes on a Plane”.) Thankfully, after judicious but liberal use of antihistamines, anti cough medicines, lozenges and anti rhinitis nasal sprays I feel better (but am still jet lagged). Did I get sick from my plane ride? Probably not.  More likely I acquired a viral infection while visiting my family and friends (and spending time in several hospitals, a university and a nursery school).

Having just gone through this I felt it would be appropriate (and easy) to share what I wrote for the Today Show in this week’s newsletter. I assume that you will be reading this at home or in your office and not on a plane….

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 (seasonal and H1N1). 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”. 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. (By the way I had mine.

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 infected 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.

What about the dry air?

The humidity within the cabin is usually below 25 percent and 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.

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.

New Bottom Line: Follow these rules, but know that lack of sleep, the stress of long distance travel and exposure to viruses and bacteria in distant places can result in illness. In my case it was blessedly brief. I plan to repeat this and many other trips. I know that immunity is not bestowed with a medical degree. I wish it were.