When a doctor pinpoints pneumonia as a patient's diagnosis, quite often he will be able to say that the disease was caused by common sources. However, in the case of Legionnaire's disease, a potentially fatal form of pneumonia, the source can now be something that the average person would least expect: using a vehicle.

Recently, a doctoral student at Arizona State University presented research to the 2014 General Meeting of the American Society for Microbiology which reveals that Legionella bacteria, the microorganisms responsible for the above mentioned respiratory illness, may thrive in windshield washer fluid.

Legionella bacteria are naturally occurring organisms in the environment and can typically be found in cooling towers of large-scale air conditioning units and hot tubs. The latest study, however, revealed that the bacteria was isolated from the windshield washier fluid of nearly 75 percent of school buses tested in a single district in Arizona.

The study's findings are particularly worrying because the Legionella bacteria cannot be transmitted from person to person, or from ingesting the contaminated water. Rather, the bacteria is transmitted via mist or vapour containing the water — fountains, showerheads, misters, nebulisers and equipment in hospitals and health care facilities would be likely sources of the bacteria.

In this case, the culprit would be aerosolised windshield washer spray. The inhaled droplets can work their way deep into the lungs and cause Legionnaires' disease. Imagine how many people are easily exposed to windshield washer fluid every day — this could potentially expose thousands of people to the bacteria each day, in various parts of the world.

Legionella bacteria flourish in warm water. In the windshield washer fluid samples taken from Arizona school buses, the bacteria thrived well because the fluid did not contain methanol, an alcohol typically used as a de-icer which would have inhibited the organisms' growth.

Otto Schwake (the Arizona State University doctoral student who presented the research) and his colleagues found that bacterial concentrations in the windshield washer fluid increased over time and they maintained stable populations for up to 14 months. It poses a danger to individuals who may be exposed to the bacteria and are more susceptible to developing Legionnaires' disease, like those with weak or impaired immune systems and the elderly.

According to Schwake, “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.”

+Duncan Hollis