"Did I catch this infection on the plane?" I wondered. I'm sure, like me, you have often asked yourself this same question, particularly if you've landed in a tropical paradise and a cold is the last thing you need. So what is the risk of picking up a bug on a plane and how can you avoid it? And should airlines add something to a certain door?

Dr. Jessica Nutik Zitter, a researcher at the University of California, San Francisco, studied 1,100 passengers travelling between San Francisco and Denver, Colorado, on planes that had newer air recirculating systems and those that use fresh air for ventilation. 21 percent of passengers aboard fresh air planes reported colds within one week, compared to 19 percent of those breathing recirculated air.

Dr. Derek Johnston, a specialist in pediatric allergy and immunology at Temple University in Philadelphia, says, "It doesn't matter if you're breathing recirculated air or fresh air. If the germs are there, you're going to get sick and it's due to confined space".

Airline officials agree the risk is proximity, and if you had 400 people sitting close together on the Trans-Siberian Railway the same number would catch colds, namely about one in five who travel in confined space.

So what can you do to avoid being the one in five that wished they had stayed home in the safety of their bed? Dr. Charles Gerba, at the University of Arizona, is an expert on what the medical community labels "fomites", namely objects that are liable to carry germs. He says the first thing to remember is that bugs are everywhere on the plane.

I always ask for an aisle seat as it's easier to get up and walk around. But Gerber says that's my first mistake as it's the seat most likely to be contaminated. Just watch people going to the bathroom and later touching every aisle seat as they steady themselves as they walk back to their seats.

Gerba relates the story of one flight. People afflicted with norovirus caused such a lineup at the bathroom the flight had to make an emergency landing. Later, a study conducted by the Center for Disease Control, showed that those sitting in aisle seats were the ones more likely to have contacted a virus.

But there is a ground zero" on every plane. The toilet, that warrants the analytical eye of a Sherlock Holmes. Next time you're on a plane do your own count, but normally there's one toilet for every 50 passengers, and on some flights one for 75. Moreover, these toilets are used by hundreds of people daily. What awaits you are fecal bacteria, norovirus, seasonal flu and the common cold.

Moreover, toilets in planes are small, making it even more difficult to perform routine hygienic measures. In fact, today with the epidemic of obesity it's hard for some people to even squeeze through the door. Add to this small sinks which makes it tedious to wash hands. Besides, Gerba cautions, even the sink may be contaminated.

Fecal bacteria can also contaminate your complimentary pillow and eating tray. In one study, Methicillin resistant Staphylococcus (MRSA), a deadly superbug, was found on 60 percent of airline trays. On a recent flight I noticed one couple cleaning their pull-down tray with Clorox wipes along with hand sanitizers.

You have to conclude that boarding a plane carries infection risks. But it's not just the fault of airlines. Humans can be their own worst enemy by failing to wash hands after a bowel movement. In one study, medical students were stationed in a public washroom during a medical convention. They reported that 50 percent of physicians left the washroom without even turning on the tap! And the convention was about infectious disease!

Here's a suggestion for airlines to help eliminate the one in five of us who develop a cold? In all my travels I've yet to see a hand sanitizer outside the plane's toilet door. Surely it would remind those who do not wash their hands to do so. It would also make my aisle seat much safer.

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