# List of Legionnaires' disease outbreaks

This is a list of Legionnaires' disease outbreaks; Legionnaire's is a potentially fatal infectious disease caused by gram negative, aerobic bacteria belonging to the genus Legionella. The first reported outbreak was in Philadelphia, Pennsylvania in 1976 during a Legionnaires Convention at the Bellevue-Stratford Hotel.
An outbreak is defined as two or more cases where the onset of illness is closely linked in time (weeks rather than months) and in space, where there is suspicion of, or evidence of, a common source of infection, with or without microbiological support (i.e. common spatial location of cases from travel history).

## Worldwide listings by year
### 1960s

| Year | City | Venue | Source | Cases | Deaths | Fatality rate | Notes |
| 1965 | Washington, D.C., United States | St. Elizabeths Hospital | Unknown | 94 | 16 | 17% | The outbreak occurred in 1965, but was not identified as legionnaires' disease until saved blood serum was exposed to bacterial samples from the 1976 Philadelphia Legionnaires' disease outbreak. |

### 1970s

| Year | City | Venue | Source | Cases | Deaths | Fatality rate | Notes |
| 1973,1977 | Benidorm, Spain | Hotel Rio Park | Shower pipes | at least 4 | 4 | unknown | The first outbreak in Hotel Rio Park occurred in 1973, four tourists died, but at the time it was not recognized as Legionnaires' disease until a subsequent outbreak in the same hotel in 1977. |
| 1976 | Philadelphia, Pennsylvania, United States | 1976 Philadelphia Legionnaires' disease outbreak | Air conditioning | 221 | 34 | 15.4% | This was the first recognized outbreak of legionellosis, although earlier cases of legionellosis were later discovered to have occurred as far back as 1947. The Philadelphia outbreak, however, had the highest death rate. |
| 1978 | Memphis, Tennessee, United States | Baptist Memorial Hospital-Memphis (1912–2000) | air-conditioning cooling tower | 44 | | | 1978 Memphis Legionnaire's Disease Outbreak |
| 1979 | Melbourne, Australia | light industrial building | medium-sized evaporative condenser | | | | |
| 1979 | Ballarat, Australia | psychiatric hospital | shower water system | | | | |

### 1980s

| Year | City | Venue | Source | Cases | Deaths | Fatality rate | Notes |
| 1985 | Wollongong, Australia | social club building | small cooling tower | | | | |
| 1985 | Stafford, England | Stafford District Hospital | Air conditioning | 175 | 28 | 16% | In April 1985, 175 patients were admitted to the District or Kingsmead Stafford Hospitals with chest infection or pneumonia. A total of 28 people died. Medical diagnosis showed that Legionnaires' disease was responsible and the immediate epidemiological investigation traced the source of the infection to the air-conditioning cooling tower on the roof of Stafford District Hospital. |
| 1986 | Adelaide, Australia | community | small cooling tower at hospital | | | | |
| 1987 | Wollongong, Australia | shopping centre | small cooling tower at a shop | | | | |
| 1988 | Adelaide, Australia | community | potting mixes | | | | |
| 1988 | Westminster, England | BBC headquarters | cooling tower at Broadcasting House | | | | |
| 1989 | Sydney, Australia | bowling club | small cooling tower | | | | |
| 1989 | Burnie, Australia | community | small cooling tower at hospital | | | | |

### 1990s

| Year | City | Venue | Source | Cases | Deaths | Fatality rate | Notes |
| 1992 | Sydney, Australia | shopping centre | small cooling tower | | | | |
| 1994 | Sunshine Coast, Australia | holiday apartment unit | private spa pool | | | | |
| 1995 | Sydney, Australia | shopping centre | small cooling tower at hospital | | | | |
| 1999 | Bovenkarspel, Netherlands | 1999 Bovenkarspel legionellosis outbreak | Hot tub | 318 | 32 | 10% | In March 1999, an outbreak occurred in the Netherlands during the Westfriese Flora flower exhibition in Bovenkarspel. 318 people became ill and at least 32 people died. There is a possibility that more people died from it (which might make it the deadliest recorded outbreak), but these people were interred before the Legionella infection was recognized. The source of the bacteria was a hot tub in the exhibition area. |

### 2000s

| Year | City | Venue | Source | Cases | Deaths | Fatality rate | Notes |
| 2000 | Melbourne, Australia | Sea Life Melbourne Aquarium | Cooling tower | 125 | 4 | 3.2% | In April 2000, an outbreak of Legionella pnemophila serogroup 1 occurred in Melbourne, Australia. The outbreak resulted in 125 confirmed cases of Legionnaire's disease, with 95 (76%) hospitalised. It is reported that 4 died from the outbreak. The investigation traced the source of the infection to the cooling tower at the newly opened aquarium. Since this outbreak, legionella infection statistics are required to be reported by the state government as a notifiable disease. Regulations were introduced by the state to control legionella in 2001. |
| 2000 | Vizela, Portugal | Public square | Decorative fountain | 11 | 0 | 0% | In August 2000, an outbreak of Legionnaires' disease occurred in Vizela, Northern Portugal. A total of 11 persons with Legionnaires' disease were admitted to the hospital. There were no fatalities. All patients had been in the main square of Vizela in the night of August 11–12, 2000, where the annual festivities of the municipality were being held. Investigators traced the source of the outbreak to a decorative fountain located in the square. |
| 2001 | Murcia, Spain | Hospital | Cooling Towers | 800+ | 6 | 0.8% | The world's largest outbreak of Legionnaires' disease happened in July 2001 with patients appearing at the hospital on July 7, in Murcia, Spain. More than 800 suspected cases were recorded by the time the last case was treated on July 22; 636–696 of these cases were estimated and 449 confirmed (so, at least 16,000 people were exposed to the bacterium) and 6 died . A case-fatality rate of approximately 1%. |
| 2002 | Barrow-in-Furness, England | 2002 Barrow-in-Furness legionellosis outbreak | Air conditioning | 172 | 7 | 4.1% | In 2002, Barrow-in-Furness in England had an outbreak of Legionnaires' disease. Six women and one man died as a result of the illness; another 172 people also contracted the disease. The cause was found to be a contaminated cooling tower at the town's Forum 28 arts centre. Barrow Borough Council later became the first public body in the UK to be charged with corporate manslaughter but were cleared. They were, however, along with architect Gillian Beckingham, fined for breaches of Health and Safety regulations in a trial that ended in 2006. |
| 2003-2004 | Pas-de-Calais, France | Petrochemical plant | Cooling tower | 86 | 18 | 20.93% | This was the worst outbreak of Legionnaires in French history. |
| 2004 | Zaragoza, Spain | Hospital | Cooling tower | 27 | 7 | 26% | Five out of seven of the fatalities were above the age of 50. |
| 2005 | Toronto, Canada | Seven Oaks Home for the Aged | Cooling tower | 127 | 21 | 16.5% | In late September, 2005, 127 residents of a nursing home became ill with Legionella pneumophila. Within a week, twenty-one of the residents had died. Culture results at first were negative. The source of the outbreak was traced to the air-conditioning cooling towers on the nursing home's roof. |
| 2005 | Fredrikstad, Norway | Factory | Air scrubber | 103 | 10 | 9.7% | At least 103 people became ill and ten died from Legionnaires' disease caused by bacteria growing in an air scrubber of a nearby factory. |
| 2007 | Jastrzębie Zdrój, Poland | 2nd District Specialist Hospital, Ophthalmic Ward | Water system | 4 | 3 | 75% | In January 2007 in the 2nd district specialist hospital in Jastrzębie-Zdrój two patients on the ophthalmic ward unexpectedly died. It was noted that they suddenly had a high fever, coughs and hallucinations. First they were transferred to the infectious diseases ward for some hours with a suspicion of pneumonia, later they were transferred to intensive care. Tests showed that both patients had legionellosis. The disease proved to be the cause of death of one of the patients, the other also had circulatory failure. The bacteria responsible for legionellosis was found in four patients from this hospital. In total the outbreak resulted in three deaths |
| 2008 | New Brunswick, New Jersey, United States | Saint Peter's University Hospital | Drinking water | 6 | 2 | 33.3% | Chlorination in the water system had dropped below effective levels. |

### 2010s

| Year | City | Venue | Source | Cases | Deaths | Fatality rate | Notes |
| 2010 | Wales | South Wales Valleys | Likely cooling towers | 22 | 2 | 9% | Thought to be cooling towers in local industry. |
| 2011 | Dayton, Ohio, United States | Dayton | Hospital air conditioning | 11 | 5 | 45% | Was the largest outbreak in Ohio since 1994 at the time. |
| 2012 | Québec City, Canada | Lower Québec City | Possibly cooling towers | 180 | 13 | 7.22% | 180 confirmed cases as of September 14, 2012, probably due to contaminated water in industrial cooling towers. |
| 2012 | Calp, Spain | AR Diamante Beach Hotel | Plumbing system | 18 | 3 | 17% | Large hotel with solar water heating system for spa and domestic hot water. A month before the deaths, local government authorities may have known about the problem, but were accused of not alerting the public to avoid disruption of the tourism industry. |
| 2012 | Edinburgh, Scotland | South west of Edinburgh | Possibly cooling towers | 92 | 4 | 3% | 56 confirmed cases, with a further 36 suspected cases, bringing the total number of people affected to 92. Four people are known to have died from the outbreak. |
| 2012 | Chicago, Illinois, United States | JW Marriott Hotel | Decorative Lobby Fountain | 10 | 3 | 30% | 8 confirmed cases with people who stayed at the JW Marriott Chicago during July–August 2012. |
| 2012 | Auckland, New Zealand | Unknown | Water Source and/or Air Conditioning | 11 | 1 | 9% | The number of people affected in a major outbreak of Legionnaires' disease in Auckland, which has claimed one life, has risen to 11. |
| 2012 | Stoke-on-Trent, England | Warehouse, Fenton | Hot tub | 19 | 1 | 5.2% | Infection began in warehouse hot tub. Seventeen of the confirmed cases visited the warehouse a couple of weeks before becoming ill. |
| 2012 | Pittsburgh, Pennsylvania, United States | Veteran's Administration Hospital | unknown | 22 | 6 | 27% | 2012 Pittsburgh legionellosis outbreak |
| 2014 | Portugal | 2014 Legionella outbreak in Portugal | Cooling tower | 375 | 12 | 3.2% | A widespread outbreak in Vila Franca de Xira district, Portugal. |
| 2015 | Bronx, New York, United States | Co-op City, South Bronx, and Morris Park | Cooling Towers in the Bronx, such as Co-op City, Lincoln Hospital, and Concourse Plaza. | 140 | 13 | 9.3% | 12 people sickened in January 2015. No fatalities reported. The 2015 New York Legionnaires' disease outbreak was investigated the New York City Health Department Out of 17 buildings with cooling towers, five tested positive for the disease, including cooling towers in the Concourse Plaza Hotel and Lincoln Hospital. The Opera House Hotel in the South Bronx is also considered a source of the outbreak. The outbreak is currently being investigated by the New York City Health Department "Environmentalists sampled 35 cooling towers in the Morris Park area, and 15 came back with positive results." In total 52 buildings were sampled and 20 of them came back positive. |
| 2015 | Northland, New Zealand | Pahiatua Fonterra Plant | Unknown | 3 | 0 | Unknown | This outbreak occurred at one of Fonterra's milk plants in Northland, New Zealand, in November 2015. Currently three cases have been reported, though currently no deaths. |
| 2015 | Quincy, Illinois, United States | Veterans home | Unknown | 58 | 13 | 27.7% | The outbreak investigation is ongoing |
| 2014–2016 | Flint, Genesee County, Michigan, United States | Countywide | McLaren Regional Medical Center | 87 | 12 | 13.8% | Investigation by Frontline also examined cases diagnosed as pneumonia that could have been misdiagnosed and diagnosed as Legionnaires' Disease. McLaren and the Michigan Department of Environmental Quality is being sued for $100 million in regards to the outbreak. See also Flint water crisis, possibly linked to legionnaires disease |
| 2016 | Sydney, Australia | Sydney Town Hall | Suspected cooling tower | at least 4 | 0 | | |
| 2016 | Hopkins, Minnesota, United States | Citrus Systems, Inc. | Cooling tower | 23 | 1 | 4.3% | Confirmed by Minnesota Department of Health. 23 people became sick, 17 were hospitalized, and one person died. |
| 2017 | Manhattan, New York, United States | Lenox Hill | TBD | 7 | 1 | 14.3% | |
| 2017 | Las Vegas, Nevada, United States | Rio Hotel and Casino | Water system | 2 | 0 | 0 | |
| 2017 | Round Rock, Texas, United States | SpringHill Suites hotel | Swimming pool and hot tub | 6 | 0 | 0 | |
| 2017 | Anaheim, California, United States | Disneyland | Cooling towers | 22 | 1 | 4.5% | |
| 2017 | Lisbon, Portugal | São Francisco Xavier Hospital | Cooling tower | 56 | 6 | 11% | In November 2017, an outbreak of Legionnaires' disease occurred in São Francisco Xavier Hospital, in Lisbon, Portugal. The outbreak resulted in 56 confirmed cases of Legionnaire's disease, of which 6 died. The investigation traced the source of the infection to a cooling tower in the hospital. |
| 2018 | Bloomsbury, London | University College London | Water cooler | 1 | 0 | | |
| 2018 | Washington Heights, New York, United States | The Sugar Hill Project (Building) | Cooling towers | 27 | 1 | 3.7% | |
| 2019 | Westminster, London, England | Dolphin Square | Water System | 3 | 0 | 0% | First case confirmed by NHS England 20 March 2019. Samples taken from the flexible shower hose and bathroom sink of the affected resident's flat, showed legionella bacteria present in those specific locations. Third case confirmed by Public Health England 1 July 2019. |
| 2019 | Evergem, Belgium | Ghent/Evergem Port Stora Enso | Cooling Towers | 32 | 2 | 6.7% | Five samples collected from 17 initially suspected cooling towers at the Port of Ghent near Evergem, tested positive for Legionella pneumophila, 3 with average and 2 in high quantities. Genetic testing confirmed 1 of 2 towers with high quantities to have links with the patients. Swedish-Finnish Stora Enso admitted to be responsible. |
| 2019 | Ohio, New Jersey and Michigan, United States | Multiple locations | Not yet determined Flint MI Water Crisis | 32 | 6 | 18.75% | As of June 4, 2019, 32 have fallen sick during the outbreaks across the states of New Jersey and Ohio. Many have fallen sick and died from drinking or being near the contaminated water in Flint, Mi. |
| 2019 | Atlanta, United States | Sheraton downtown | | 11 | 0 | | Legionnaires' Disease Outbreak May Have Sickened Dozens in Atlanta |
| 2019 | Fletcher, North Carolina, United States | North Carolina Mountain State Fair | hot tub display | 141 | 4 | | Four People Have Died From A Legionnaires' Outbreak Linked To A Hot Tub Display At A State Fair Legionnaires' outbreak linked to hot tub display kills third North Carolina fairgoer N.C. Officials Trace 124 Legionnaires' Disease Cases To Hot Tub At A Fair Investigation of an Outbreak of Legionellosis in Western North Carolina |

### 2020s

| Year | City | Venue | Source | Cases | Deaths | Fatality Rate | Notes |
| 2020 | Vernon Hills, Illinois, United States | Brookdale Senior Living | Under investigation | 5 | 1 | 20% | Outbreak of Legionnaires' disease up to five reported cases at Vernon Hills senior living center. Number Of Legionnaires Cases Rises To Five At Brookdale Vernon Hills Senior Living Facility. |
| 2020 | Vila do Conde, Póvoa do Varzim, Matosinhos, Porto District, Portugal | Multiple locations | Under investigation | 88 | 15 | 17% | 88 cases and 15 deaths (11 of these were also infected with SARS-CoV-2). The source of the bacteria is still unknown. The deadliest Legionella outbreak in Portugal, it was declared extinct on January 13, 2021. |
| 2022 | San Miguel de Tucumán, Tucumán Province, Argentina | Health clinic | Under investigation | 22 | 6 | 27% | Cluster of pneumonia cases associated with a health clinic. 22 cases and 6 deaths (all with comorbidities). The source of the bacteria is still unknown. |
| 2023 | Rzeszów, Subcarpathian Voivodeship, Poland | Multiple locations | Under investigation | 164 | 41 | 25% | Ongoing outbreak. The source of the bacteria is suspected to be contaminated water sources. |
| 2024 | Lincoln, New Hampshire, United States | RiverWalk Resort | Cooling Tower | 5 | 0 | 0% | |

## Governmental controls to prevent outbreaks
### Regulations and ordinances

The guidance issued by the UK government's Health and Safety Executive (HSE) now recommends that microbiological monitoring for wet cooling systems, using a dipslide, should be performed weekly. The guidance now also recommends that routine testing for legionella bacteria in wet cooling systems be carried out at least quarterly, and more frequently when a system is being commissioned, or if the bacteria have been identified on a previous occasion. Further non-statutory UK guidance from the Water Regulations Advisory Scheme now exists for pre-heating of water in applications such as solar water heating systems.
The City of Garland, Texas, United States requires yearly testing for legionella bacteria at cooling towers at apartment buildings.
Malta requires twice yearly testing for Legionella bacteria at cooling towers and water fountains. Malta prohibits the installation of new cooling towers and evaporative condensers at health care facilities and schools.
The Texas Department of State Health Services has provided guidelines for hospitals to detect and prevent the spread of nosocomial infection due to legionella. The European Working Group for Legionella Infections (EWGLI) was established in 1986 within the European Union framework to share knowledge and experience about potential sources of Legionella and their control. This group has published guidelines about the actions to be taken to limit the number of colony forming units (i.e., the "aerobic count") of micro-organisms per mL at 30 °C (minimum 48 hours incubation):
| Aerobic count | Legionella | Action required |
| 10,000 or less | 1,000 or less | System under control. |
| more than 10,000 up to 100,000 | more than 1,000 up to 10,000 | Review program operation. The count should be confirmed by immediate re-sampling. If a similar count is found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions. |
| more than 100,000 | more than 10,000 | Implement corrective action. The system should immediately be re-sampled. It should then be 'shot dosed' with an appropriate biocide, as a precaution. The risk assessment and control measures should be reviewed to identify remedial actions. |
Almost all natural water sources contain Legionella and their presence should not be taken as an indication of a problem. The tabled figures are for total aerobic plate count, cfu/ml at 30 °C (minimum 48 hours incubation) with colony count determined by the pour plate method according to ISO 6222(21) or spread plate method on yeast extract agar. Legionella isolation can be conducted using the method developed by the US Center for Disease Control using buffered charcoal yeast extract agar with antibiotics.
Copper-Silver ionization is an effective industrial control and prevention process to eradicate Legionella in potable water distribution systems and cooling towers found in health facilities, hotels, nursing homes and most large buildings. In 2003, ionization became the first such hospital disinfection process to have fulfilled a proposed four-step modality evaluation; by then it had been adopted by over 100 hospitals. Additional studies indicate ionization is superior to thermal eradication.
A 2011 study by Lin, Stout and Yu found Copper-Silver ionization to be the only Legionella control technology which has been validated through a 4-step scientific approach.
It was previously believed that transmission of the bacterium was restricted to much shorter distances. A team of French scientists reviewed the details of an epidemic of Legionnaires' disease that took place in Pas-de-Calais in northern France in 2003–2004. There were 86 confirmed cases during the outbreak, of whom 18 died. The source of infection was identified as a cooling tower in a petrochemical plant, and an analysis of those affected in the outbreak revealed that some infected people lived as far as 6–7 km from the plant.
A study of Legionnaires' disease cases in May 2005 in Sarpsborg, Norway concluded that: "The high velocity, large drift, and high humidity in the air scrubber may have contributed to the wide spread of Legionella species, probably for >10 km."
In 2010 a study by the UK Health Protection Agency reported that 20% of cases may be caused by infected windscreen washer systems filled with pure water. The finding came after researchers spotted that professional drivers are five times more likely to contract the disease. No cases of infected systems were found whenever a suitable washer fluid was used.
Temperature affects the survival of Legionella as follows:
   * 70 to 80 °C (158 to 176 °F): Disinfection range
   * At 66 °C (151 °F): Legionellae die within 2 minutes
   * At 60 °C (140 °F): They die within 32 minutes
   * At 55 °C (131 °F): They die within 5 to 6 hours
   * Above 50 °C (122 °F): They can survive but do not multiply
   * 35 to 46 °C (95 to 115 °F): Ideal growth range
   * 20 to 50 °C (68 to 122 °F): Growth range
   * Below 20 °C (68 °F): They can survive but are dormant
Removing slime, which can carry legionellae when airborne, may be an effective control process.