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Guess where researchers found the bacteria that cause Legionnaires’ disease?

File photo of school bus. Researchers have discovered that Legionella bacteria can live in some brands of windshield washer fluid and flourish in the motor vehicle reservoirs that contain it. They looked at samples taken from school buses. (Washington Post staff/File)

In 1976, a previously unknown strain of bacteria killed 34 people and sickened more than 200 after an American Legion convention in Philadelphia. The bacteria were traced to the cooling towers in the hotel's air conditioning system and named  Legionella for the bicentennial convention at which the deadly outbreak occurred.

Since then, regular outbreaks of Legionnaires' disease have occurred around the world, and researchers have learned that the bacteria live in water, soil and elsewhere. The greatest danger is when water containing the bacteria becomes an inhalable aerosol that can work its way deep into the lungs, causing a pneumonia that is sometimes fatal. More often, it causes Pontiac fever, a milder, flu-like illness that runs its course.

Now a researcher at Arizona State University has discovered that the bacteria can live in some brands of windshield washer fluid and flourish in the motor vehicle reservoirs that contain it. When sprayed, some of the droplets can be inhaled by vehicle occupants, especially people like bus drivers who are behind the wheel for extended periods.

Otto Schwake, a doctoral student who conducted the research and is presenting his findings this week at a meeting of the  American Society for Microbiology, said he believes Legionella is under-diagnosed as the cause of pneumonias in the United States. One study in Britain cited windshield washer fluid for nearly 20 percent of Legionnaires’ disease cases not associated with hospitals or outbreaks.

"When a doctor sees pneumonia, he’s not going to say 'oh you got it from your car'. He’s going to say 'oh you got it from a typical source'," Schwake told me Sunday.

Schwake's team tested five different brands of washer fluids. Especially disturbing: all were taken from school buses. In Arizona there is typically no need to add methanol, an alcohol used as a de-icer, to the washing fluid. The bacteria, which flourish in warm water, grew well in washer varieties without methanol, which would inhibit their growth.

Other potential sources of Legionella are misters, fountains, nebulizers and hospital equipment that create fine water droplets as their main function. Schwake said he believes transmission of the bacteria from soil will  become a recognized problem in the next 20 years.

"The big take-home message is that this is one example, one pathogen, with a potential new route of exposure that we're not aware of," he said. "But microbes are everywhere."