Legionella (Legionnaires' risk from wiper water)

“Windscreen wiper water may be the cause of 20% of cases of Legionnaires' disease in England and Wales,” the BBC warned. It reported that the Health Protection Agency (HPA) has said that simply adding screenwash to wiper fluid kills the bacteria and could save lives.
The news story is based on the results from a preliminary study by the HPA. Researchers carried out a case-control study, surveying the driving habits and known risk factors of the 75 surviving Legionnaires’ patients whose infection was community acquired between July 2008 and March 2009 in England and Wales. They also surveyed a matched control group to see which exposures were more common in those with disease. They calculated that about 22% of infections in people under 70 could be attributed to being in a car without screenwash.
The HPA says more research is needed to see whether using screenwash could help prevent the disease and that they are looking into this. This may be preliminary research, but in the meantime it may be advisable for drivers to use screenwash to avoid this unproven, yet plausible risk.
What is the news based on?
The news story is based on the results from a preliminary study by the HPA. The study was carried out by researchers from the HPA in partnership with researchers from the European Centre for Disease Prevention and Control in Sweden, and Bristol University. It was published in the European Journal of Epidemiology.
What did the research involve?
This case-control study was carried out by the HPA to investigate the possible risk factors for Legionnaires’ disease in the UK. The study was commissioned after an unusually high number of cases were reported in England and Wales in 2006 (334 community acquired infections). Around this time, an analysis concluded that professional drivers were five times more likely to get Legionnaires’ than people from other occupations. The HPA aimed to corroborate these findings and to further explore the possible reasons for the difference between the occupations.
The researchers contacted the 75 surviving cases who had acquired Legionnaires’ disease in England and Wales between July 12 2008 and March 9 2009 through a community infection. They also included 67 control people without the disease, who were matched with the 75 cases based on their area of residence, sex and age.
The participants were sent a questionnaire asking about their driving habits, other known risk factors and potential infection sources in the vehicles. They were asked what type of car they drove, its age, service history, content of the wiper fluid reservoir and whether their driving was for social or work reasons.
The questionnaires results were analysed, taking into account gender, age, smoking and the season. This showed that two factors were linked with an increased likelihood of being infected: driving through industrial areas and driving or being a passenger in a vehicle that used windscreen wiper fluid without screenwash.
Can you get Legionnaires’ disease from your car?
The HPA’s study is well reported and has found a strong association between people who do not use screenwash and the risk of Legionnaires’ disease.
This is a case control study and so cannot prove causation, but the researchers say there is a plausible biological association. They say that it is conceivable that the bacteria grow in the stagnant water of the wiper’s fluid reservoir, which then becomes an aerosol when it is sprayed onto the windscreen.
This study is small and there may be some limitations in the way the data were analysed as it was not possible to match the pre-planned three controls with every Legionnaires’ case.