May car washing represent a risk for Legionella infection?

Legionella is a ubiquitous Gram-negative bacterium naturally found in aquatic environments. It can pose a health problem when it grows and spreads in man-made water systems. Legionella pneumophila is the most common cause of Legionnaires' disease nowadays, a community-acquired pneumonia with pulmonary symptoms and chest radiography no different from any other form of infectious pneumonia. Legionella monitoring is important for public health reasons, including the identification of unusual environmental sources of Legionella.

We report two cases of Legionnaires' disease associated with two different car wash installations in the province of Vicenza, in the Veneto region, northeastern Italy. Patients were not employees of the car wash installations, but users of the service. In both cases, Legionella antigen was detected in urine using the Alere BinaxNOW® Legionella Urinary Antigen, and Legionella antibodies were detected in serum using SERION ELISA classic Legionella pneumophila 1-7 IgG and IgM. Water samples were also analyzed as part of the surveillance program for Legionella prevention and control in compliance with the Italian guidelines.

Both patients had clinical symptoms and chest radiography compatible with pneumonia, and only one of them had diabetes as a risk factor. Legionella urinary antigen and serological test on serum samples were positive for Legionella in both patients, even if much slighter in the case A due to the retrospective serological investigation performed a year later the episode and after the second clinical case occurred in the same district. The environmental investigations highlighted two different car wash plants as potential source of infection. A certified company using shock hyperchlorination was asked to disinfect the two plants and, subsequently, control samples resulted negative for Legionella pneumophila.

Any water source producing aerosols should be considered at risk for the transmission of Legionella bacteria, including car wash installations frequently used by a large number of customers and where poor maintenance probably creates favorable conditions for Legionella overgrowth and spreading. Additional research is needed to ascertain optimal strategies for Legionella monitoring and control, but environmental surveillance, paying careful attention to possible unconventional sources, should remain an important component of any Legionnaires' disease prevention program. Additionally, all available diagnostic methods would be recommended for the confirmation of all cases even in the event of non-serogroup 1 Legionella pneumophila infection, probably underestimated at this time.