Examining the Presence Legionella in Car Washer Fluid: Study Results

Otto Schwake, PhD, Department of Civil and Environmental Engineering at Virginia Tech, discusses the findings of his team’s study exploring Legionella in car washer fluid.

Interview Transcript (slightly modified for readability).

“With the field study, [our findings] were pretty simple, pretty straightforward. It was a big undertaking, a lot of samples, a lot of logistics, but the results are pretty simple. Basically, going from Arizona being the hottest place we sampled, down to North Dakota being the coldest, [there was] a relatively clean trend: the warmer it was, the more often we found Legionella, and, to some extent, the more there were there. Not significant differences, but the numbers for the 3 warmest climates were much higher than anywhere else we saw the Legionella.

[Those were summer results; when we repeated our sampling in winter,] we figured temperature was going to be a factor [and] people [were] going to be more likely to use higher concentrations of methanol in their washer fluid during the winter. We only found Legionella in our hottest site, in Arizona; so, in winter, everywhere else got freezing temperatures, we didn’t find any culturable Legionella. Based on those results, we were thinking, ‘hey, our hypothesis is kind of filling out.’ It makes sense; [cold] temperature, more methanol. Hot temperature is good for Legionella, less methanol is good for them, so warmer climates are better.

Now, the results get a little tricky for our bench experiment because almost the exact opposite happened. Without going too much into detail, [there’s] a lot of data to go through, but given the big results, when we incubated them in the same washer fluid from Michigan, one of our cold weather sites, and washer fluid from our Arizona site, they survived better in the Michigan washer fluid than the Arizona washer fluid, even though the Michigan washer fluid had 35% methanol by volume. So, very high methanol concentration.

When we were first starting this study, we saw very high die-offs in any washer fluids with methanol, which we figured makes sense; it’s an alcohol. Many bacteria, at least Legionella, have trouble being in a solution with a lot of alcohol; it does a lot of harmful things to their cells. So, we figured, they’re dying; that makes sense. Except in our Michigan washer fluid, they weren’t dying, and eventually everyone else died off, even our positive control. In just plain tap water that we had, they started eventually dying off, which we’re thinking, ‘okay, something funny is going on.’ We repeated it [and] the same deal. That was with culturing.

When we looked closer, basically we performed microscopy on these guys [and] we could tell if they were alive but sort of in a hibernation state, in a dormant state, where they didn’t want to grow, and that was what was happening. So, across the board, except for the highest, highest concentrations of methanol, very little depth was occurring in these Legionella. They were just becoming stressed out to the point where they didn’t want to grow, but they weren’t dying in any sort of huge way.

[Looking at] our Arizona samples, that looked like they died off very quickly, almost entirely there, [but] in our Michigan samples, they were alive, they weren’t dying, they just were healthier to the point that they were able to grow. Why that happened, we don’t know.

One other interesting piece of data that came out of the study, and [is] sort of a big point for some of our follow-up work that we want to look at, was the methanol concentration in the sample that had the best survival rate in the Michigan washer fluid, it decreased. We’re not 100% positive, but they went from about 35% down to about 15%, so noticeable, measurable, potentially biologically relevant decrease in methanol concentration. We have no idea why; it was basically washer fluid [that] had been sitting on our shelf at room temperature for months before we used it, it didn’t decrease hardly any in concentration. We incubated it with just Legionella, same temperature, same conditions, and it decreased. So, why that happened, it was almost a side note; we weren’t really predicting anything to happen to the methanol, we just wanted to make sure the concentrations were as they were on the label, but it decreased, so, that’s maybe an interesting result that came out of [the study].