New research from the UK suggests that as many as 1 in 5 of community-acquired sporadic cases of Legionnaires’ disease occur as a result of not adding screenwash, which normally contains anti-bacterial agents, to windscreen wiper fluid in cars and vans.

The study was the work of researchers at the UK’s Health Protection Agency (HPA), and you can read a paper about it in the 7 June online first issue of the European Journal of Epidemiology.

Legionnaires’ disease is a rare type of pneumonia caused by bacteria from the genus Legionella that live in water. In 2008, there were 359 cases reported in England and Wales, mostly in men, and 40 per cent were overseas travel-related. This study focused on Legionnaires’ disease acquired in the community, as people go about their daily lives, as opposed to cases where exposure most likely occured during foreign travel.

In their background information, co-author Dr Isabel Oliver, regional director of the HPA South West, and colleagues, wrote that it is not easy to find a source of infection of sporadic cases of Legionnaires’ disease, but they noticed that in England and Wales, professional drivers were five times more likely to have it than other people and decided to explore the possible risk of exposure for drivers and passengers.

They carried out a case control study that included all the surviving community acquired sporadic cases in England and Wales that started with symptoms between mid July 2008 and early March 2009.

They contacted the cases by phone and then from their details recruited consenting matching controls. All who consented to take part in the study filled in questionnaires about their driving habits, potential sources of infection in vehicles and other known risk factors.

When the researchers analysed the results, they had data on 75 cases and 67 controls. They found that:

  • Two exposures linked vehicle use with an increased risk of Legionnaires’ disease.

  • One was driving through industrialized areas (odds ratio OR 7.2, 95 per cent confidence interval CI ranged from 1.5 to 33.7).

  • The other was travelling in a vehicle where no screenwash had been added to the windscreen wiper fluid (OR 47.2, 95 per cent CI 3.7 to 603.6).

The researchers concluded that:

“Not adding screenwash to windscreen wiper fluid is a previously unidentified risk factor and appears to be strongly associated with community acquired sporadic cases of Legionnaires’ disease.”

They suggested that around 1 in 5 of community acquired sporadic cases of Legionnaires’ disease could be attributed to this exposure, and a simple way to reduce the risk of transmission of Legionella bacteria in the community would be for people to make sure they add screenwash to the windscreen wiper fluid in their vehicles.

According to a BBC report, the HPA also conducted a pilot study where they found 1 in 5 cars without screenwash carried traces of Legionella while none of the cars that had screenwash had the bacteria.

Professor Hugh Pennington, a well known expert in bacteriology, told the BBC it made sense to recommend that people make sure they have screenwash in their cars. Legionella is a bug that takes advantage of warm water systems that are not cleaned out, and if something this simple can prevent people catching the disease, then “it’s a no brainer really”, he remarked.

There are more than 40 species of Legionella bacteria, with L. pneumophila most commonly associated with Legionnaires’ disease. Although naturally occuring in lakes, rivers and reservoirs, and can lie dormant at low temperatures, the bacteria thrive in temperatures between 20 and 40 degrees C and can colonise manufactured water systems, where they feed on the scale, sediment, sludge and various bio-films that build up.

To be hazardous to humans Legionella bacteria need to be present in sufficient numbers and to be pathogenic, some strains being more infectious than others. They are usually transmitted via tiny water droplets, for instance in showers and air conditioning units, and person to person transmission is not thought to be a way to catch the disease.

Symptoms usually appear between two and ten days after infection, although in rare cases it may take longer. Illness starts with fever, muscle ache, headache, dry cough, and shortness of breath, and develops into pneumonia. Some people may also experience diarrhea, vomiting, confusion and delirium.

Most patients improve with treatment which includes antibiotics, but in the more vulnerable cases, such as the elderly or the already sick, severe illness, respiratory or systemic failure and shock can happen. Among otherwishe healthy people, the death rate is between 10 and 15 per cent.

According to figures produced by the European Working Group for Legionella Infections, in 2006, there were 6,280 cases of Legionnaires’ disease reported from 35 countries in Europe.

“Windscreen wiper fluid without added screenwash in motor vehicles: a newly identified risk factor for Legionnaires’ disease.”
Anders Wallensten, Isabel Oliver, Katherine Ricketts, George Kafatos, James M. Stuart and Carol Joseph.
European Journal of Epidemiology, published onlinefirst 7 June 2010.
DOI: 10.1007/s10654-010-9471-3

Additional sources: BBC, NaTHNaC, HPA.

Written by: Catharine Paddock, PhD