Milan, November 18 (Adnkronos Health) – It likes heat and humidity and prefers water pipes and air conditioning, because it reproduces faster. Legionellosis is an infection caused by the bacterium Legionella pneumophila, known to have more than 60 different species divided into 71 serotypes, which caused a form of pneumonia called Legionnaires’ disease in 1976, after an epidemic spread among attendees of an American Legion meeting at the Bellevue Stratford Hotel in Philadelphia. On that occasion, 221 people contracted the disease, with 34 deaths. The source of contamination was identified as the hotel’s air conditioning system. This pathology is now making headlines again in Milan, where 11 cases have been recorded in the San Siro area (all people who had predisposing risk factors for infection, according to the ATS), one person has died and, currently, 8 people are hospitalized.
In Italy, as reported by the Higher Institute of Health in an online focus, over the last thirty years the number of legionellosis cases has continued to increase, even though the disease is underestimated. In 2022, there were a total of 3,111 cases of legionellosis reported, with an increase of 14% compared to the previous year, and after 2 years, returning to pre-Covid pandemic values. The following year, in 2023, according to a publication in the national epidemiological bulletin, the reports received by the ISS Infectious Diseases Department further increased: 3,911 surveillance cards were linked to the same number of legionellosis cases (up 25% compared to the previous year). 74.9% of these infections were reported by 6 Regions: Lombardy, Emilia Romagna, Tuscany, Veneto, Lazio, and Piedmont, and 25.1% by 15 other Regions/Pa. The crude incidence rate of legionellosis nationally in 2023 is 66.3 cases per million population, an increase compared to the previous year (52.8/1,000,000), also higher than the value before the Covid pandemic. And we continue to observe a North-South gradient with raw incidence values of 96.6 cases per million in the North, 67.5 per million in the Center, and 19.9 per million in the South.
More than 70% of patients were at least 60 years old, 69.2% were men and the male-to-female ratio was 2.2 to 1. Of the 3,911 reported cases, 7.8% had stayed at least once in a place other than their usual home (hotel, campsite, boat, private home), 3.2% had been hospitalized, 2.7% had been in a closed community (nursing home, health care home, rehabilitation facility), 1.4% had traveling and living abroad. 84.4% of cases were classified as community origin, i.e. the origin was unknown. 66% of patients had comorbidities, mainly chronic degenerative. Among the 2023 cases, 125 nosocomial cases were also reported (3.2% of the total), i.e. infections in hospitals.
Legionella – recalls the ISS – is present in natural and artificial aquatic environments: springs, including hot springs, rivers, lakes, mudflats. From this environment they reach the artificial environment, such as city pipes and building water systems, such as tanks, pipes, fountains and swimming pools, where they can act as amplifiers and dispersers of microorganisms, thereby creating situations of potential risk to human health.
Legionellosis is usually transmitted via the respiratory route, through inhalation, aspiration or microaspiration of aerosols containing legionella, or particles originating from drying. “Droplets can form due to spraying of water or air bubbles in them, or due to impacts on solid surfaces,” the experts recall. And the danger of these water particles is inversely proportional to their size (smaller diameter droplets reach the lower respiratory tract more easily). Cases of legionellosis acquired through wounds have also been reported in the literature. Overall, human disease remains rare; “The attack rate during epidemic outbreaks is low, less than 5%,” experts said. Finally, the infection-related mortality rate depends on several specific factors (such as the severity of the disease, the appropriateness of initial antibiotic treatment, the site of infection contracted, the patient’s previous condition) and can vary from 40-80% in untreated immunosuppressed patients, to 5-30% if the pathology is appropriately treated. Overall, the death rate from legionellosis is between 5% and 10%, the ISS concluded.
There are two forms of legionellosis that can occur: true Legionnaires’ disease, which often includes a more acute form of pneumonia, and the less serious Pontiac fever. The first, after an incubation period that varies from 2 to 10 days (average 5-6), in the most serious cases it can appear suddenly with fever, chest pain, shortness of breath, cyanosis, productive cough, while in less serious cases it can develop slowly with fever, malaise, pain, mild unproductive cough. Gastrointestinal, neurologic, and cardiac symptoms are occasionally present, and changes in mental status are common. Pontiac fever, after an incubation period of 24-48 hours, manifests in an acute flu-like form without lung involvement, and resolves in 2-5 days. Clinical symptoms are: malaise, myalgia, and headache, followed quickly by fever, sometimes accompanied by cough and red throat. Diarrhea, nausea, and mild neurological symptoms such as dizziness or photophobia may appear. Treatment of legionellosis, as a disease of bacterial origin, primarily involves antibiotic therapy. Regarding prevention, it is important to “properly design and implement technological systems that involve heating or spraying water (systems at risk)”, highlight the ISS experts, and “implementation of preventive measures (maintenance and, if necessary, disinfection)” to counter the multiplication and spread of bacteria in systems at risk.
