Legionellosis is a highly lethal disease caused by some types of Legionella, among which the most frequent and sadly famous is certainly Legionella pneumophyla.
The first case of epidemic described in the Bibliography is quite recent and dates back to 1976, the year in which a group of former American Legion fighters participated in a conference at the Westin Hotel in Philadelphia, in the United States. The name of the microorganism derives from Legion and the pathology derived from it was called "Legionnaires' disease".
Since then, unfortunately, cases of Legionella have multiplied in the world, so much so that special surveillance by the WHO (World Health Organization) has become necessary with the establishment in 1986 of a special European Institute dedicated to this purpose, the EWGLI, in which Italy is also present with the Istituto Superiore di Sanità.
In 2002 alone, approximately 675 cases of Legionella were reported to EWGLI, mostly acquired in tourist accommodation facilities. Characteristics of Legionella, its spread in nature and symptoms of the disease. 42 different types of Legionella have been described and approximately 50% of them are capable of causing the disease in humans.
High concentrations may be found in poorly maintained piped water systems or air conditioning systems consisting of cooling towers, evaporative condensers, or air humidifiers. The disease typically begins with fever, chills, headache, dizziness, photophobia, and muscle pain, followed by a dry cough and difficulty breathing, which in some cases progresses to severe pneumonia. Nearly a third of those affected also have diarrhea or vomiting, and about 50% have confusion and delirium.
The fatality rate is 10-15% of those affected. The incubation period usually ranges from two to ten days, and symptoms appear on average between three and six days after exposure.
Legionella enters our body through the respiratory tract, through inhalation or aspiration of aerosols. The smaller the water droplets, the easier the germ can reach the lower respiratory tract, especially the lungs.
The aerosol can be generated by various sources: turning on a tap or shower in the presence of contaminated water systems, hot tubs and swimming pools; Turkish baths and sauna areas; ornamental fountains especially if located indoors; garden irrigation systems, waste water from toilets, cooling towers and evaporative condensers, air conditioning systems in general.
To date, it has never been demonstrated that the disease can be contracted by drinking contaminated water and direct transmission between humans seems to be excluded, while cases of legionellosis linked to accidental contamination of wounds have been reported.
How to prevent risks
Legionella species has been classified as biological agent 2 Annex XI of Law 626/94, that is, as an agent capable of causing an infectious disease in humans but which has little chance of spreading in the environment if the appropriate prophylactic or therapeutic measures are implemented.
Prevention is therefore to be considered the fundamental moment to avoid the spread and multiplication in the environment of this germ, as also underlined in the Document of guidelines for the prevention and control of legionellosis of 4 April 2000 – Permanent Conference for relations between the State, the Regions and the Autonomous Provinces of Trento and Bolzano. Below is a brief scheme of implementation of the prevention systems.
Internal plumbing
General characteristics required: - clear separation between hot water pipes and cold water pipes; - avoid installing or having pipes with blind thermal sections and without water circulation; - avoid the formation of stagnant water; - ensure that the water systems are cleaned periodically.
Technical characteristics: - the temperature of the cold water must be less than or equal to 20°C in every part of the system; - the temperature of the hot water must be equal to or greater than 60°C in the tank; - the temperature of the hot water must be equal to or greater than 50°C at the tap (it must be “hot” to the touch).
Basic preventive measures: - let hot and cold water flow from the terminals for a few minutes at least once a week; - eliminate the blind terminal sections and modify any hydraulic sections that form stagnant water; - establish the dates for cleaning the system at least twice a year; - periodically remove limescale deposits from the terminals (shower bulbs, aerator, etc.); - check the temperature of the cold water with a certified thermometer; - analyze the cold water and treat it with chlorine 50 mg/liter if the Legionella values are greater than 1,000 cfu/liter.
Basic preventive measures: - check the environmental humidity with a calibrated hygrometer; - carry out correct annual maintenance that includes: - regular annual cleaning and disinfection of the cooling towers and evaporative condensers of the air conditioning units; - regular annual cleaning and disinfection of the fan coils with final microbiological check; - a monthly inspection of the cooling towers and visible pipes; - eliminate any rust and visible algae in the air conditioning system.
Following the actions implemented, it is advisable to carry out a microbiological check: a) For the water system: - of the cold water used; - of the hot water from the tanks, taps and showers; - of the encrustations and/or organic residues collected in the terminal ampoules of the showers or taps.
b) For the air conditioning system: - of the water in the cooling towers. Subject it to chlorination treatment if the Legionella values are greater than 1,000 cfu/liter; - of spot fan-coils per floor or accommodation facility;
c) of the humidification sections of the air conditioners.
The results will indicate whether the preventive actions have been effective and therefore any corrective actions to be taken.
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