In December 2019, the Public Health Agency of Barcelona (PHAB) received a case report of Legionnaires’ disease in a 59-year-old man. Onset of symptoms had begun a week before diagnosis. On December 13, the patient sought care at a hospital, and a diagnosis of Legionnaires’ disease was made by UAT. A respiratory sample was not available because of the lack of productive secretions. The patient was hospitalized briefly, and his clinical course was unremarkable. After discharge, he completed the remaining course of antimicrobial drug therapy and proceeded favorably to cure.

After the case was reported, public health nurses contacted the patient to complete a structured epidemiologic questionnaire that included demographic data, personal risk factors, activities, and potential exposures during the 14 days before illness onset. The patient smoked and had a medical history of hypertension and type 2 diabetes. He worked as a commercial truck driver, and his driving route included merchandise pickup at an industrial area once a day. The truck used for work was self-owned; the patient had purchased it secondhand ≈1.5 years before illness. He reported that the vehicle had been unused for several months before the purchase and denied using screen wash in the windshield wiper fluid.

No other cases of Legionnaires’ disease reported during the same period were related to his residence or driving areas. Two weeks after the interview, environmental inspectors from PHAB sampled the fluid that remained in the windshield wiper tank of the truck. The 2,000-mL sample of water was collected and stored in a sterile container (Deltalab, https://www.deltalab.es) treated with sodium thiosulfate. The PHAB laboratory analyzed the sample for L. pneumophila. Culture results using Legionella selective media, according to the ISO 11731:2017 protocol (https://www.iso.org), were negative. However, the sample was also analyzed by using real-time PCR (Appendix). Testing showed that the fluid was PCR positive for L. pneumophila (Table). Laboratory test results and cleaning procedures to follow for the windshield wiper tank were explained to the driver. Public health inspectors also recommended adding screen wash fluid to the windshield wiper fluid regularly.

On September 17, 2020, a new case of Legionnaires’ disease was detected by UAT in commercial truck driver. A respiratory sample was unavailable because of lack of respiratory secretions. The patient was a 58-year-old man who smoked and had a medical history of recently diagnosed chronic obstructive pulmonary disease. He was hospitalized briefly and was successfully treated with antimicrobial drug therapy. His driving routes included industrial areas frequently located within Barcelona. No further cases that could be epidemiologically linked to this case were identified during the same period.

The patient used the truck daily and denied adding screen wash to the windshield wiper fluid; he also reported that the windshield wiper fluid had not been changed for >6 months. On the basis of previous case experience, we obtained a sample of the windshield wiper fluid. Analysis of the sample was performed in the PHAB laboratory according to the stated standards. Although we were unable to detect L. pneumophila by culture or real-time PCR, Legionella spp. was detected by culture at a concentration of 6.3 × 10³ CFU/L (Table). Consequently, public health inspectors recommended cleaning procedures to disinfect the windshield wiper tank, together with adding screen wash fluid to the windshield wiper fluid regularly.

We report 2 sporadic cases of Legionnaires’ disease in commercial truck drivers in which the laboratory findings were consistent with, but not exclusive to, the windshield wiper fluid as the source of infection. The etiologic agent was presumed to be L. pneumophila serogroup 1 (Lp1) because both patients were given a diagnosis by UAT, which detects only Lp1. DNA of L. pneumophila (unknown serogroup) was found in the windshield wiper fluid for the first case, and Legionella spp. was cultured from the fluid for the second case. Although the presence of Lp1 was not confirmed in the windshield wiper fluid for either case, laboratory findings indicated that the flid was a potential source for both cases.

Previous studies have identified windshield wiper fluid without screen wash as a potential risk factor for Legionnaires’ disease (4). Furthermore, 2 previous studies have identified Legionella spp. in windshield wiper fluid (8,9), confirming that the bacteria can survive in this medium and the fluid as a possible source of infection. These results are consistent with our observations for the windshield wiper fluid for the second case described. Despite these observations, transmission from this source has not been epidemiologically confirmed. Our findings strengthen the epidemiologic connection between windshield wiper fluid as a source of infection for truck drivers.

Several vehicle-related sources have been described as confirmed or potential sources of Legionnaires’ disease, although these sources were infrequently considered and difficult to investigate (3,10,11). Kanatani et al. identified L. pneumophila in road puddles (12) and hypothesized that bacteria reach the windshield wiper fluid tank through road splashes. Alternatively, Legionella spp. could reach the tank after a car wash at a contaminated installation or through a contaminated water source used to fill the tank. Warm temperatures or heat radiated from the motor of the vehicle to the water tank, along with lower or absent methanol levels in screen wash fluid, and water stagnation could favor bacterial proliferation in the windshield wiper fluid tank.

Beyond routinely investigating this source, especially in commercial truck drivers, a simple measure of adding screen wash to the fluid can be recommended. This action has the potential benefit of decreasing the risk for infection by inhibiting growth of Legionella spp. growth through a bactericidal effect of screen wash components, such as propanol/methanol (9).

In summary, our results indicate that windshield wiper fluid is a potential source of sporadic Legionnaires’ disease, especially in commercial truck drivers, and should be routinely investigated. A simple recommendation of adding screen wash to windshield wiper fluid or emptying the tank when the vehicle is unused for several months is a preventive measure likely to be effective and should be adopted by drivers.