Legionella Control and Risk Management
The term Legionellosis refers to all the serious forms of pneumonia caused by more than 40 species of aerobic bacteria belonging to the genus Legionella. They are ubiquitous microorganisms very present in humid or hot or aqueous environments, the most dangerous of which is Legionella pneumophila, which is responsible for about 90% of all cases of disease.
The disease was first identified following a major epidemic in 1976 in a group of former American Legion fighters (hence the name of the disease) who attended a conference at the Westin Hotel in Philadelphia, USA.
Since then, on the basis of the WHO Guidelines, a system of surveillance of the disease has been activated in many countries. In Italy, for cases of legionnaires’ disease, with DM Salute 15/12/1990, the compulsory notification in class II in SIMI (Sistema Informativo delle Malattie Infettive e diffusive) is foreseen.
Legionella has been isolated in civil and industrial water-sanitary and aeraulic systems of old construction or with inadequate maintenance or, in some cases also from the natural water of rivers, lakes and storage tanks.
The disease develops in two forms of different severity: the actual legionnaire’s disease, which frequently includes an acute form of pneumonia, and Pontiac fever, a much less severe form.
The incubation period usually ranges between 2-10 days and symptoms occur on average between 3-6 days after exposure, initially with fever, chills, headache and muscle pain, followed by dry cough and breathing difficulties which in some cases progress to severe pneumonia.
About 30% of those affected are also affected by diarrhoea or vomiting and about 50% by mental confusion and delirium, with an average lethality rate of 10-15% that exceeds 60% in infants or elderly people and in transplanted or immunosuppressed patients. To date, it has not been demonstrated that the disease can be contracted by drinking contaminated water and direct human transmission seems to be excluded.
Legionnaires’ disease is generally contracted by the respiratory tract, by inhalation or microaspiration of aerosols in which the bacterium is contained. These aerosols are formed through the tiny drops generated by the spray of water, or by the impact of water on solid surfaces. The smaller the droplets are, the more dangerous they are (eg: drops of water with a diameter < 5μ reach more easily the lower respiratory tract and become invasive).
Aerosols that are hazardous to health can be generated by favorable environments, characterized by poor use, maintenance and neglected sanitization, such as, for example:
- water storage tanks;
- breakwater of shower taps and shower heads;
- whirlpools, swimming pools, saunas, Turkish baths;
- hydro fans, humidifiers, air conditioners, split, fan coils;
- UTA batteries, cooling towers, evaporative condensers, air treatment systems;
- irrigation systems for parks and gardens;
- waste water from hygienic systems.