No, this is not an essay about emissions, or seatbelts, or fatal car accidents. It’s something more unexpected and surprising.

First (You know me by now.), we need a little history lesson.

In July 1976, (Happy Bicentennial!), there was a convention of 4000 people- veterans and their families who were members of the American Legion- at the Bellevue-Stratford Hotel in Philadelphia. Shortly after the convention ended, many attendees developed severe pneumonia. In all, 221 people were sickened, and 34 of them died. This mystery “monster killer” made headline news across the nation. People were terrified. Media quickly named it “Legionnaires’ disease”. Poor Bellevue-Stratford Hotel; it closed only a few months later; no one would make a reservation there. (Can you blame them?)

There was a massive investigation by the CDC and the Pennsylvania Department of Health. For months, there were no leads, and no clue to what had caused this frightening illness. Seven long months later, CDC microbiologist Joseph McDade identified a totally new bacterium in the lung tissue from one of the victims. This newly discovered bacterium was named Legionella, after the outbreak among the members of the American Legion. Eventually, epidemiologists figured out the bacteria had been living and multiplying in the rooftop air conditioning cooling tower at the hotel and spreading through the air conditioning ducts.

Interestingly, after this bacterium was discovered and the link to water containers was understood, researchers went back and analyzed samples from previous unsolved pneumonia outbreaks, and found evidence of Legionella as far back as 1943! As research has continued over the 50 years since the American Legion outbreak, scientists have learned a lot about Legionella. All environmental sources have been related to water. During outbreaks, it has been isolated from cooling towers, shower stalls, condensers, even drinking water in plumbed buildings. Legionella is fairly resistant to chlorine, and can easily multiply in water as warm as 107°. (As an aside, car air conditioners, central air conditioners and home window units are closed-loop systems and do not harbor Legionella.) Person-to-person transmission has never been documented. It can be treated with Erythromycin, a common antibiotic.

There are now stringent regulations for water-containing building systems. Maximum and minimum temperatures, mandated residual disinfectant levels, frequency of testing for Legionella, and a mechanical maintenance program are all mandated. In spite of that, Legionella persists and there are sporadic outbreaks globally.

There are about 10,000 cases/year in the US. The vast majority of them end up being linked to contaminated water in cooling towers, but there have been other interesting sources. A 2017 outbreak at Disneyland was eventually linked to the cooling tower that held the water released as overhead mist to cool visitors to the park. A 2019  outbreak at the North Carolina Mountain State Fair was caused by bubbling water from a hot tub exhibit. Four people died.

OK, so here’s where your car comes into the story. Over 15 years ago, Swedish scientists at the Swedish Institute for Infectious Disease Control realized that long-distance truck drivers are at 5-fold higher risk for Legionnaires’ disease, but it was not clear why that is. It was assumed that the culprit was cooling towers in truck stops, office or factories they delivered to or picked up loads from, or other common water sources. The truckers filled out exhaustive questionnaires; nothing unusual panned out. In a deep dive into the epidemiological data, only one activity stood out; using windshield wiper fluid that was just water (no cleaner added) was associated with developing Legionnaires’. The researchers estimated over 20% of cases could be linked to this! More recently, Spanish researchers at the University of Barcelona were trying to trace the source of Legionella in some truck drivers. Their research showed the same thing and in addition, they were able to grow Legionella from the windshield washer tanks.

Perhaps the Legionella got into the windshield washer tanks from splashes from the road, or from going through car washes, or a contaminated water hose used to fill the water tank. Either way, the warmth from the engine would keep the water at a perfect temperature for growing Legionella.

Think about it. When was the last time you added windshield cleaner to your washer tank? Or did you just pour some water in there? And we have all turned the windshield washers on with our car window or convertible top down and gotten sprayed in the face, haven’t we? Yikes!

Thankfully, there is an effective and simple solution. Always use windshield washer solution (not plain water) and make sure the product you buy contains methanol, which will kill Legionella. Careful though, methanol has a slightly sweet taste and is highly toxic, so store it out of reach of children and pets.

So, no, even if your car is a 1958 Plymouth Fury named Christine, a la Stephen King’s thriller, it isn’t really trying to kill you. It just wants some windshield washer fluid!