Wednesday, April 29, 2009

How flu is transmitted aboard passenger airliners (Not the way you may think!)

by B. N. Sullivan

sneezeUnfortunately, many people are beginning to panic about the present outbreak of the H1N1 Swine Flu virus, and that is causing a ruckus in the commercial air transport industry. Crews and passengers alike are worried that they will 'catch' the virus on board a plane. Are they right to be so concerned?

I can't completely allay people's fears, but I can relate some scientific information that may help to put the relative risk of catching the swine flu virus on an airplane into perspective. Let me tell you about some things that are known about just how is flu transmitted aboard an aircraft.

Many seem to believe that people aboard passenger aircraft catch the flu and other infectious diseases because much of the cabin air is recirculated. In other words, they believe that the viruses and bacteria that cause infectious diseases are airborne, and that the germs are distributed throughout the aircraft via the recirculated air.

More and more evidence shows this explanation to be false, or at least limited. For one thing, the HEPA filters used in the air circulation systems of modern passenger aircraft are amazingly efficient at trapping particles -- including viruses and bacteria -- before they can be recirculated. But there is another reason, too.

Countless studies -- most of which have been carried out in health care facilities, where there are lots of germs of all kinds -- have shown that infectious diseases are transmitted most often through direct contact with surfaces on which droplets from the sneezes or coughs of an infected person have landed. When droplets land on surfaces, the viruses and bacteria contained in them stay on the surface, even after the droplets dry.

The germs are passed to the hands of other people who subsequently touch those surfaces. This is exactly why frequent and thorough hand washing is so highly recommended as a method of infection control.

Recent information about how flu is transmitted, published in a journal called Lancet Infectious Diseases [reference below], confirms that flu transmission "occurs at close range rather than over long distances, suggesting that airborne transmission, as traditionally defined, is unlikely to be of significance." This conclusion is based on a large-scale review of published data on the subject.

Results from 32 experimental and epidemiological studies were evaluated by a Canadian team from the University Health Network, Toronto for this report. Their analysis showed that the flu virus is indeed more likely to be transmitted to people within a short distance of the infected person, via large respiratory droplets that fall out of the air, and not via "fine aerosols" that hang in the air for extended periods of time.

This information has important implications for crews working aboard passenger aircraft -- especially flight attendants. On the one hand, it is somewhat reassuring to know that the risk for airborne transmission of the flu virus throughout an aircraft is relatively small. On the other hand, it adds more importance to avoiding close contact with an infected person -- and with objects that may have been contaminated by "large respiratory droplets" from that person -- that is, from coughs and sneezes, as well as oral and nasal secretions in general.

The passengers sitting nearest to an infected person are those most at risk for coming into contact with surfaces contaminated by "respiratory droplets" -- seats, tray tables, armrests, and so on. For flight attendants, the greatest risk probably comes from handling items used by an infected person, or from that person's immediate area.

Risk Mitigation

Flight attendants who touch or handle items that have been used by infected people may very readily come in contact with the germs left behind by those "respiratory droplets." Collecting trash, food trays, and other items used by an infected person can put flight attendants at risk for coming into direct contact with infectious agents.

The sensible thing to do would be to wear protective gloves when handling items used by infected passengers. Unfortunately it's not always clear who is infected and who is not. Therefore, if I were running the show (especially during an active outbreak), I would advise flight attendants to wear protective gloves whenever they are collecting used items, and I wouldn't restrict the use of gloves to collecting trash or food trays.

Unfortunately not all air carriers approve of flight attendants wearing gloves, except when they are tending to a passenger who is known to be infected. The trouble is that during an active outbreak such as the present one, it is difficult to know who is infected, and who is not. In fact, people can be infected -- and infectious -- before they begin to feel or display symptoms.

A number of airlines actually prohibit their cabin crew from wearing protective gloves -- on the silliest grounds, I might add. For example, I have been told that some airline managers think that the sight of a flight attendant wearing protective gloves would upset the passengers, because it would suggest that the aircraft was unclean. This is nonsense, and it trivializes a known health risk -- a risk that exists for other passengers, as well as cabin crew.

If you work for a carrier that prohibits or discourages cabin crew from wearing gloves -- especially when collecting food trays and trash -- I would advise you to bring up the issue with your inflight supervisors. Get your union involved, too.

Transmission of infectious diseases aboard an aircraft is an occupational health risk for crews that should not be ignored, yet there are ways to lessen the risk.

Earlier this week, the Association of Flight Attendants-CWA, the largest flight attendant union in the U.S., published a page on their website, Swine Flu: What flight attendants need to know, which includes useful information about the virus that currently is circulating, and ways that cabin crew can protect themselves. Go and have a look at that, as a starting point.

Stay informed about current developments, but choose your information sources wisely. Don't rely solely on news reports, some of which may be inaccurate or have a bias. In the United States, the best source of current, reliable information is the Centers for Disease Control and Prevention (CDC). Here is the link to the CDC's Swine Influenza (Flu) website:

Another place to look for both background information and current news about the current outbreak is the News & Info About H1N1 Swine Flu page on the website.

Study referenced above: Brankston, G., Gitterman, L., Hirji, Z., Lemieux, C., & Gardam, M. (2007). Transmission of influenza A in human beings. The Lancet Infectious Diseases, doi:10.1016/S1473-3099(07)70029-4.