EVAPORATIVE TOWERS AND LEGIONNAIRES’ DISEASE, PART 1
Closely linked to the proper maintenance of the evaporative towers and air conditioning systems in general, the problem of Legionnaires’ disease has returned in an alarming manner of topicality given the recent cases of infection recorded in the province of Brescia (Italy): the Italian Institute of Health reports an increase of 17% in cases of legionnaires’ disease in 2017 in Italy, up from 1,700 recorded in 2016.
Legionella is a bacterium (there are indeed at least 40 different species) whose ideal habitat is represented by water with the presence of oxygen at temperatures ranging from 25 to 50 ° C. This bacterium is widespread in nature, (ponds, lakes), while in anthropogenic environments, it can be present in mechanical systems, in water and sanitation networks (showers, humidifiers, pipes …) and in cooling / conditioning systems especially in the presence of evaporative towers: the transmission of Legionella occurs by inhalation of aerosols, which is why it is more likely to contract legionnaires’ disease in buildings served by air conditioning and humidification systems.
The diseases caused by this bacterium are Legionnaires’ disease and Pontiac fever.
The first recorded epidemic episode of Legionnaires’ disease occurred in July 1976, in a hotel in Philadelphia during the annual gathering of members of the American Legion, hence the term “Legionnaires’ disease” assigned to the morbid form described on that occasion. The episode occurred in the form of an acute febrile pulmonary manifestation, with a mortality of 16%. After careful serodiagnostic and environmental tests, the bacterium responsible for the epidemic was identified and called Legionnaires’ disease pneumophila. Legionnaires’ disease had multiplied inside the cooling tower which, placed on the roof of the building, sprayed aerosol near the intake point of the air conditioning system. The air conditioning system had thus been contamined, and the aerosol spread through the vents into the various rooms during the conference, causing an airborne infection of the many occupants.
In Italy, the first outbreak of legionnaires’ disease was reported in 1980, in a small hotel on the Adriatic coast, where 23 cases occurred, 2 of which were fatal; Legionnaires’ disease pneumophila was isolated from the hotel’s water system. Other epidemic outbreaks were subsequently described in hospitals, hotels and welfare facilities.
By Francesco Viola, Thermodynamic Engineer
Sources:
Guidelines for the prevention and control of Legionellosis, edited by the Italian Ministry of Health
Eurovent, Guidelines on how to maintain efficient and safe cooling systems
