Motorists who do not add screen wash solution to the water used to wash their windscreens, risk getting potentially deadly legionnaires' disease, a study revealed this week.

In 1976 an outbreak of pneumonia occurred in members of the American Legion (an ex-servicemen’s organisation) attending a conference at the Belview Stratford Hotel in Philadelphia. After much investigative work, the cause was shown to be a bacterium named Legionella pneumophila, an organism which had not previously been recognised. We now call this illness Legionnaire's disease.  This bacterium has been found to most commonly affect those people over the age of fifty; affects more men than women and more commonly, those who are smokers.  It causes a pneumonia, which can be fatal, (roughly 10% of people affected by this disease die from complications), but which in most cases, will respond to appropriate antibiotics.

It has now been shown that motorists are at risk from the illness, which they can catch from the water in their windscreen washers.  This water, which is, by definition, stagnant , and usually warmed by the engine or the environment, is the perfect place for the organism to flourish.  When the water is sprayed out on to the windscreen, droplets may be inhaled by the driver or passengers if the vehicle windows are open; or by passers-by, into the lungs, where the infection can then establish itself.

Prompt diagnosis, differentiating it from other similar illnesses, is essential if the disease is to be treated appropriately.

The warning comes after health experts discovered that professional drivers were five times more likely to be infected with the dangerous bug, which is found in warm, stagnant water.

Drivers are now being urged to add screen wash to the container water after traces of the legionella bacterium were found in one in five cars that did not have the additive, but in no cars that did.

It is feared that around 20% of legionnaires' cases could arise from such exposure.

The findings come from a Health Protection Agency-led study, which looked at why people at the wheel were more likely to be infected. Most at risk were found to be those driving a van, people who drive through industrial areas, and people who often had the car window open.

But the "most intriguing" higher-risk group was drivers not using screen wash, which kills off the legionella bug, the study authors found.

They said: "Not adding screen wash to windscreen washing fluid is a previously unidentified risk factor and appears to be strongly associated with community- acquired sporadic cases of legionnaires' disease.

"We estimated that around 20% of community acquired sporadic cases could be attributed to this exposure."

The report, which was published in the European Journal of Epidemiology, added: "This simple public health advice may be of worldwide relevance in reducing morbidity and mortality from legionnaires' disease."

The disease is contracted when small droplets of contaminated water are breathed in and the bacteria have also been identified in the vapour from showers and from air-conditioning units.  It cannot spread from person to person.

There were 345 cases in England and Wales last year, although some infections were caught overseas.