What is it?
Legionella are aerobic gram-negative bacilli. The first known outbreak of Legionnaires disease was at an American Legion Convention in 1976. There are 30 distinct species of Legionella, but only four have been associated with outbreaks. The Legionella pneumonia form 14 sero-groups with sero-group 1 accounting for 70% of infections. These bacteria can be found in a natural environment of soil or water, and also domestic water supplies and air conditioning units, but rarely causes problems. It favours stagnant water and temperatures between 20°C and 45°C. It has not been known to be passed on from person to person.
How is it spread?
The bacteria are spread by airborne droplets being inhaled into the respiratory tract. This can lead to legionnaires disease causing acute pneumonia or Pontiac Fever. Pontiac Fever is a mild form of legionnaires disease and resembles an allergic reaction rather than an infection. The reservoir is likely to be pooled water such as in air conditioning units. Whirlpool spas and even fountains have been implicated in outbreaks. There is an incubation period of 2-10 days.
Symptoms
Legionella presents with pneumonia like symptoms, such as shortness of breath, expectorating, fever of up to 40°C, anorexia and sometimes-abdominal pain and diarrhoea. The patient may be able to identify a history of water droplet inhalation for example from household humidifiers or even water-cooling systems. It can be fatal and the mortality rate will be higher in those with compromised immunity, therefore hospital outbreaks can be serious. Very rarely patients may develop septicaemia, respiratory failure, renal failure and liver disease.
Prevention
Chlorination, temperature maintenance and cleaning of water devices or systems where water can pool, can all be used to help control the multiplication of the legionella bacillus. Large constitutions such as hotels and hospitals have a duty under Health and Safety Executive to carry out regular analysis on their water supply to ensure decontamination and maintenance of systems.
References
Ayliffe G, Fraise A, Geddes A, Mitchell K 2000
Control of Hospital Infection – A Practical handbook 4th Edition
Arnold London
Health & Safety Executive: Approved Code of Practice L8 – Legionnaires Disease: The control of legionella bacteria in water systems
Health & Safety Executive: Technical Guidance HSG 274 HSG Parts 1, 2, 3 and HSG 282.
Health Technical Memorandum 04-01 Safe water in healthcare premises Parts A, B, C and D
