Legionnaires’ disease: An explanation
Legionnaires’ disease was named after 182 delegates at a convention of the American Legion in Philadelphia in 1976 became ill, with 28 of them dying. Theories as to the cause abounded, including suggestions of mass poisoning, and it was two or three years before the responsible agent – a bacterium called Legionella pneumophilawas identified.
The usual manifestation of Legionella infection is pneumonia, an inflammation of the lungs that can reduce the amount of oxygen entering the bloodstream. Symptoms of Legionnaire’s disease are consequently very similar to those seen in other forms of pneumonia – fever, coughing, breathlessness, pain and headaches are all common symptoms, with diarrhoea and a feeling of confusion also sometimes being present. As with any pneumonia, the functioning of other organs in the body can become impaired if the attack is a severe one. Anyone can catch Legionnaire’s disease, but it is rare in children and most commonly occurs in middle age, while men are affected more than twice as often as women. Smokers are at greater risk than non-smokers.
Legionella bacteria are very widespread, and can be found almost anywhere where there is water, but only some strains result in disease in humans. Very roughly, there are about 500 recognised cases of Legionella pneumonia in the UK each year, although it is probable that many milder episodes go undiagnosed. Unlike (for instance) influenza, Legionnaire’s disease is not transmitted from person to person. Most sufferers of the disease appear to be single, isolated cases unconnected to others and the source of infection is usually not identified. As a consequence of its association with water, though, installations like air conditioning systems, humidifiers, showers and Jacuzzis may fall under suspicion. A significant minority of cases, though, do appear to be linked suggesting a common source of infection, and in such cases a particularly vigorous search must be made to identify that source and eliminate it.
The diagnosis is most commonly made by a urine test which detects products of the bacteria, but it can easily be missed and so the routine first-line treatment of all individuals with pneumonia bad enough to require admission to hospital should include antibiotics active against the Legionella bacterium. Most people will make a full recovery, but as many as 10% of diagnosed cases in the UK may die, with the greatest risk to the elderly and those with other medical problems. As well as antibiotics, support for the lungs is given by means of additional oxygen to breathe and in the severest cases artificial ventilation by machine may be necessary.
Prevention of Legionnaires’ disease is challenging, but substantial steps have been taken in recent years in the design of installations involving water to reduce the risk of colonisation by Legionella, and there are rules regarding both the maintenance of such installations and their regular checking to ensure that Legionella bacteria are not present. It is unlikely, though, that it will be possible in the foreseeable future to prevent all cases so engineers, front-line clinicians, laboratory staff and public health specialists must continue to be acutely aware of the dangers that Legionnaire’s disease can pose.
Dr John Moore-Gillon, Honorary Medical Adviser, British Lung FoundationTagged in: disease, health, infection, Legionnaires' disease, nhs
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