BOSTON — Windshield washer fluid, sprayed by drivers to help see out of their car windows, may be a breeding ground for bacteria that causes the deadly pneumonia known as Legionnaires’ disease.
Previous studies have tied riding in automobiles to the illness, though researchers didn’t know how or why it happened. An investigation into fluid dispersed by school buses in Arizona seems to have provided the answer, according to research released Sunday by the American Society for Microbiology at its meeting in Boston.
Three quarters of the buses tested in one district in Arizona were positive for the bacteria, the study found. When the contaminated fluid was sprayed, the researchers detected levels of the bacteria that spread within a range that could be contracted and cause outbreaks of Legionnaires’ disease.
“Washer fluid has the traits a potentially dangerous source of Legionella exposure needs,” Otto Schwake, a microbiology Ph.D. student at Arizona State University in Tempe and the study’s lead author, said in an e-mail. “It is aerosolized, heated and people are regularly exposed to it. The results from this study support previously demonstrated epidemiological evidence for a link between automobiles and Legionnaires’ disease by providing microbiological data on survival, presence and transmission of Legionella in washer fluid.”
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Sunday’s study is the first to find the bacteria Legionella in an automobile’s washer fluid and aerosolized in the spray, Schwake said.
The Legionella bacteria are found naturally in the environment, most commonly in water. They are associated with hot tubs and cooling towers found in large-scale air conditioners and are transmitted through a mist or vapor, not person to person.
The airborne bacteria are contracted by inhaling small drops of contaminated water. Cases often involve air conditioning and heating systems in buildings or public showers. The disease was named after an outbreak at a meeting of the American Legion in Philadelphia in 1976.
Most of the people exposed don’t become sick, the authors said. Those most at risk include the elderly, smokers and those with weakened immune systems, Schwake said.
The researchers in the study first measured Legionella survival by growing samples of the bacteria in washer fluid in the lab. They then examined Legionella in washer fluid collected from school buses in central Arizona.
They found that the amount of Legionella in the washer fluid was higher in the summer than winter months.
Researchers are working on a model to calculate the risk of Legionnaires’ disease from windshield washer spray. Schwake said more data is needed before any safety precautions can be given.
“We are exposed to an enormous number and variety of microbes every day from countless sources, the overwhelmingly vast majority of which are harmless,” he said. “That being said, unknown sources of pathogen transmission certainly exist and need to be studied. Due to the sheer lack of data, I believe any study examining the relationship between Legionella and automobiles would be greatly useful.”