LEGIONELLA AND LEGIONNAIRES' DISEASE

 Legionella is the name given to the group of bacteria which give rise a number of illnesses, including Legionnaires' disease – a potentially fatal pneumonia type of infection of the lower respiratory tract. Legionellosis is the term given to the group of diseases caused by the bacteria and include other less serious diseases such as Pontiac & Lochgoilhead fever.

Legionella bacteria occur naturally and are widespread in the natural environment. They are present in all watercourses such as rivers, lakes and reservoirs and can even be washed in through the mains supply. Such bacteria have most probably been around for thousands, if not millions of years, and have only started to cause problems in the last 70 years or so due to the way water is used and stored in the modern environment.

One of the key things to remember in assessing risks and managing Legionella is that the bacteria must physically enter the lungs in order for someone to contract Legionniare’s disease. To do this the water must be in a fine mist or spray, usually referred to as an ‘aerosol’. To put this into context, imagine having a shower – it is not the droplets that hit you on the head we are interested in but the fine mist that forms in front of your eyes. There is no substantive evidence that the disease can be contracted through drinking contaminated water or indeed that it is contagious.

The bacteria were first isolated following an outbreak of the then unnamed disease at the Bellevue Hotel in Philadelphia. Shortly after their annual American Legionnaire’s conference dinner a large proportion of the Legionnaire’s became ill and it was suspected that some form of food poisoning was to blame. However, a number of passers by also become unwell and this quickly ruled out anything form of poisoning.

An investigation followed and it was eventually discovered that the source of the bacteria was a cooling tower on the roof of the hotel. Cooling towers use the heat loss associated with the evaporation of water to provide cooling, a side effect of this process is water vapour – usually referred to as drift in the context of a cooling tower.

At the Bellevue Hotel the cooling tower was used to provide the cooling for the air conditioning and was sited next to the main air intake for the system. The contaminated drift was passing straight from the tower into the main air conditioning duct but also down the side of the hotel hence the cases in passers by. This was the first the bacteria was isolated and became known as Legionnaire’s Disease.

Over the past 8-10 years statistics show there have been an average of 200-300 reported cases each year, of which there is a 10 – 12% mortality rate. Since 2002 there has been a steady rise and annual figures now top the 550 mark.

It is widely accepted that the problem is significantly worse than this. EWGLI (European Working Group Legionella) study cases on a Europe wide basis and support numbers around 10 times higher than this in the UK. To add weight to this argument, recent studies suggest that Legionella could be responsible for up 2 – 3 % of Community Acquired Pneumonia (CAP). CAP records figures for pneumonia type infections caught from people living their day to day lives, there are 150,000 cases of CAP per annum and 98% are never attributed to a cause.

 From the graph below it can be seen that there is a much higher incidence in males, in fact the statistics reveal that men are 3 times more likely to catch Legionnaires' Disease than females. The usual argument put forward for this is that more males are engaged in engineering / plumbing but studies have revealed that this predispostiion is more likely to be genetic.

What are the symptoms?

From the point of initial infection, the typical gestation period is between 2-10 days. In most cases, symptoms begin after 5-6 days. 

The above symptoms present 2 issues;