The named species of Legionella have been isolated from environmental sources or patients, and their names reflect either the place where they were found or the person who discovered them. Some of the environmental species have not yet been shown to cause human disease.
Legionnaire’s Disease Causes and Symptoms
Most infections with legionellas are respiratory, although other infections can occur, such as wound infections due to contact with contaminated water. The commonest result of infection is an acute pneumonia, Legionnaires disease.
After an incubation period of two to ten days the patient begins to feel ill with malaise, general aches, a headache, and a dry cough. Within a day or two their temperature may reach 40OC and patients may become confused and seriously ill. The signs and symptoms may be more those of a septicaemia (a reaction to bacteria in the blood) than respiratory illness, but after another day or two it becomes obvious that the patient has severe respiratory infection.
Patients may develop complications such as thrombocytopenia (a deficiency of blood elements required for blood clotting), acute renal failure, or failure of other important organs. The organism may spread via the bloodstream and cause infection elsewhere in the body. Abdominal symptoms such as nausea, vomiting and diarrhoea are quite common.
Mortality from Legionnaire's
Legionnaires disease is a potentially fatal condition; in the United Kingdom in 1996, the mortality rate was 12%. The disease is treated with antibiotics (such as erythromycin), plus supportive treatment including mechanical ventilation if necessary.
About half the cases occurring in the UK are associated with travel abroad, the destinations most frequently associated with Legionnaires disease are (in descending order) Spain, France, Turkey and Greece which are popular destinations for British holidaymakers.
Travel associated cases are now reported by European countries to a central reporting scheme run by the Communicable Disease Surveillance Centre in London, so that outbreaks occurring in one country but involving the citizens of several nations can be detected and acted upon as quickly as possible.
There are a number of risk factors for Legionnaires disease. The disease is commoner and/or more severe in men, cigarette smokers, elderly patients, those with pre-existing lung disease and patients with deficient immune systems.
Legionellas in Water Supplies
Legionellas are commonly found in small numbers in collections of fresh water, but there they probably do no harm. They can survive normal drinking water disinfection, and may enter the mains water supply for homes and industry. Once in the distribution system, they may multiply (particularly if the water temperature is favourable or if the system contains excessive sediment) and susceptible people may be exposed to the organism via sprays generated by water taps or shower heads.
Prevention of Legionnaire’s Disease
Person to person transmission is virtually unknown. Legionellas in the water supply or in air conditioning systems may be almost impossible to eradicate, but a series of control measures is recommended. Hot water should be stored at very high temperatures, although this may be difficult to achieve in older hot water systems which cannot be relied upon to store all the hot water at a consistent temperature.
Air conditioning plants, including cooling towers and humidifiers, must be examined and cleaned regularly and all cooling towers must be registered with the local authority. Biocides and anti-scaling compounds may be added to the water.
Water fittings and washers should not be made of material which encourages the growth of the organisms, and water distribution systems should be designed to avoid dead-ends which case water stagnation and allow multiplication of the organism.
Source:
The National Health Service online
