The Legionnaires' disease

In 1976 at a gathering of volunteer soldiers (legionaries) in Philadelphia, USA, 220 bystanders were infected by an unknown disease.

Symptoms of the disease initially resembled those of an ordinary flu (fatigue, high fever, headache, muscle pain and cough) and then progressed into pneumonia, which resulted in 34 people losing their lives.
Fueled by this tragic chain of events, the virus legionella was discovered which was caused by the bacterium legeonella which was found "nested" in air conditioners and broadcast through the air into the respiratory system of the attendants.
Even today, a large number of people are afflicted with this disease, especially during the summer months and exhibit these symptoms. Mortality rates to date range between 12 ~ 15% of patients and the outcome depends mainly on the state of the immune system of the patient.
The bacterium legionella develops in filters and elements of air conditioners and in the airways of larger installations with central air distribution. Besides air conditioning, the bacterium legionella can occur even in the distribution of hot water networks however the treatment and prevention vary and go beyond the scope of this article.
Contamination of the air conditioning units can be prevented by frequent maintenance of the installation unit and the chemical cleaning of sensitive points where the microbe usually grows (cooling elements, filters, nozzles, ducts).