The bacterium that causes Legionnaires' disease — an uncommon kind of pneumonia that can be deadly — can grow in the windshield washer fluid that's used in cars, a new study suggests.
In the study, researchers found that the bacterium Legionella, normally found in freshwater, can survive in car windshield washer fluids and grow in washer-fluid reservoirs. People could become infected with the bacteria when they come in contact with the fluid, the researchers said.
In fact, the bacteria can survive in windshield-washer fluid for anywhere between a few days and several months, depending on the kind of fluid, the researchers said. And, in one particular type of fluid, the bacteria survived longer than they did in sterile water.
"Washer-fluid spray can release potentially dangerous numbers of these bacteria into the air," study author Otto Schwake, a doctoral student at Arizona State University, said in a statement.
Prior to the study, it was known that the bacteria could be present in the mist from air conditioners, hot tubs and showers, among other sources, but scientists hadn't investigated whether the bacteria could live in washer fluid.
Now, "These results suggest that automobiles may serve as a source of transmission for Legionella infections," Schwake said. [5 Things You Should Know About Legionnaires' Disease]
As many as 18,000 people in the United States are hospitalized yearly for Legionnaires' disease, according to the Centers for Disease Control and Prevention. However, most people exposed to the bacteria do not become sick; older people and those with weakened immune systems are more likely to become ill.
In the study, the researchers examined windshield fluid from Arizona school buses and found that, in nearly 75 percent of the buses, the fluid was contaminated with the bacteria.
The researchers measured the levels of the bacteria in washer fluid in a laboratory, and grew samples of bacteria in the fluid.
Although windshield washer fluid is rarely associated with the spread of Legionnaires' disease, previous research found that people who drive may have a higher risk of Legionnaires' disease than people who don't drive. In one study, researchers found that almost 20 percent of cases of Legionnaires' disease in the United Kingdom that were not related to hospitals or outbreaks were associated with car windshield washer fluid.
The high levels of the bacteria that the researchers found in windshield washer liquid may be attributed, in part, to Arizona's warm climate, which provides a good environment for these bacteria to survive, as they thrive in heat.
"While potential transmission of a deadly respiratory disease from a source as common as automobile windshield washing systems is significant, the study also points to the fact people can be exposed to pathogens — particularly those occurring naturally in the environment — in previously unknown and unusual ways," Schwake said.
The study was presented May 18 at the 2014 general meeting of the American Society for Microbiology.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.