Invisible, but formidable. Since 1976, legionellosis has regularly hit by waves, recalling the fragility of our water and air conditioning networks. From Philadelphia to Albertville, via New York or Murcia, each epidemic left a painful trace. Here are the most striking outbreaks of this still unknown disease.
Legionellosis: a disease in the tragic name
In July 1976, in Philadelphia, hundreds of American Legion veterans participated in an agreement. In a few days, 221 fall seriously ill and 34 die.
A few months later, researchers identify the responsible bacteria, Legionella pneumophilagiving this atypical pneumonia the name of “legionellosis”, in memory of the affected veterans. This founding episode remains one of the most symbolic, both by its magnitude and by the anxiety it has aroused.
Large epidemics of legionellosis
Since this inaugural drama, the legionellosis has not stopped reappearing.
- 1976, Philadelphia (United States)
During a veterans congress, 221 people are contaminated after inhaling the air of an infected air conditioning system. Thirty-four deaths are identified. It is the first documented great epidemic. - 1985, Stafford (United Kingdom)
A city hospital becomes the home of major contamination. 175 patients contract the disease and 28 lose their lives. The event draws attention to the dangerousness of poorly maintained hospital facilities. - 1999, Bovenkarspel (Netherlands)
During a horticultural exhibition, jacuzzi systems exposed to the public spread the bacteria. 318 people fall ill and 32 die, making this episode one of the deadliest in Europe. - 2001, Murcia (Spain)
More than 800 cases are identified, probably linked to contaminated air conditioning systems. It is the most massive epidemic ever recorded in Western Europe, but fortunately with a low mortality rate. - 2003, Toronto (Canada)
In a retirement home, 23 residents die after contracting the legionellosis. The investigation points to poor maintenance of hot water pipes. This episode raises a debate on the safety of establishments for the elderly. - 2005, Pas-de-Calais (France)
A paper factory located in Harnes is identified as a source of contamination. 86 cases are confirmed, including 18 deaths. The case shakes France and pushes to strengthen industrial controls. - 2012, Edinburgh (Scotland)
An important home bursts in an industrial area of the city, affecting 92 people. The origin is attributed to poorly maintained aerorefrigerant towers, confirming their major role in the spread of the bacteria. - 2015, New York (United States)
The Bronx is struck by a disturbing outbreak: 138 infected people and 16 dead. The cooling towers of a hotel are incriminated. The episode triggers a large infrastructure cleaning plan throughout the city. - 2018, Harlem (Netherlands)
Thirteen cases are reported and a patient dies. Again, contamination is attributed to water installations. This epidemic recalls that even small cities can be affected. - 2022, Pisa and other regions (Italy)
Several dozen cases are identified in different areas of the country, often linked to hotels and tourist infrastructure. The episode arouses concerns in a country very frequented by travelers. - 2025, New York (Harlem)
Since the beginning of August, five people have died in Harlem after contracting a legionellosis, according to the New York Health Department. The survey carried out on site revealed the presence of bacteria in several towers of the area. - 2025, Albertville (France)
The Savoyard city is faced with 17 confirmed cases and a death. The epidemic, still under analysis, brutally recalls the dangerousness of the legionellosis, often confused with covid due to similar symptoms.
A threat not to underestimate
What makes legionellosis particularly formidable is its resemblance to other respiratory infections such as the flu or the COVID-19. Fever, cough, fatigue: the first signs easily deceive, delaying the diagnosis.
The disease is not contagious from human to human, but it can be fatal in the most fragile. Its treatment is based on antibiotics, effective only if administered quickly.
The legionellosis is not contagious between humans, but its late diagnosis can make it fatal. The past flambés show how the bacteria hides in our daily environments.
Rigorous maintenance of hot water networks and air conditioning systems is the only weapon to prevent these tragedies. And each epidemic, from yesterday to today, recalls that vigilance must remain constant.
Each epidemic reminds us of the need for rigorous maintenance of water networks and increased vigilance in public places, to prevent history from being repeated.