List of Legionnaires' disease outbreaks

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Legionellosis is a potentially fatal infectious disease caused by gram negative, aerobic bacteria belonging to the genus Legionella.[1][2] The first reported outbreak was in Philadelphia, Pennsylvania in 1976 during a Legionnaires Convention at the Bellevue-Stratford Hotel.[3]

Worldwide listings by year[edit]

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 it time was not recognized as Legionnaires' disease until a subsequent outbreak in the same hotel in 1977.[4]
1976 Philadelphia, Pennsylvania 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.[5][6][7]
1979 Melbourne, Australia light industrial building medium-sized evaporative condenser [8]
1979 Ballarat, Australia psychiatric hospital shower water system [8]
1985 Wollongong, Australia social club building small cooling tower [8]
1985 Stafford, England, United Kingdom 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 [8]
1987 Wollongong, Australia shopping centre small cooling tower at a shop [8]
1988 Adelaide, Australia community potting mixes [8]
1989 Sydney, Australia bowling club small cooling tower [8]
1989 Burnie, Tasmania community small cooling tower at hospital [8]
1992 Sydney, Australia shopping centre small cooling tower [8]
1994 Sunshine Coast, Australia holiday apartment unit private spa pool [8]
1995 Sydney, Australia shopping centre small cooling tower at hospital [8]
1999 Bovenkarspel, Netherlands 1999 Bovenkarspel legionellosis outbreak Hot tub 318 32 10% In March 1999, an outbreak in the Netherlands occurred 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.[9][10]
2000 Melbourne, Australia Melbourne Aquarium Cooling tower 125 4 4.2% 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.[11] Since this outbreak, legionella infection statistics are required to be reported by the state government as a notifiable disease.[12] Stringent Regulations were introduced by the State to control legionella in 2001.[13]
2001 Murcia, Spain Hospital 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, UK 2002 Barrow-in-Furness legionellosis outbreak Air conditioning 172 7 4.1% In 2002, Barrow-in-Furness in the U.K. suffered 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.[14] 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.
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, which is not unusual as L. Pneumophila is a fastidious bacteria, meaning it leaves virtually no trace of itself. 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 56 10 17.8% 56 people became ill and ten died from Legionnaires' disease caused by bacteria growing in an air scrubber of a nearby factory.
2008 New Brunswick, New Jersey Saint Peter's University Hospital Drinking water 6 2 33.3% Chlorination in the water system had dropped below effective levels.[17]
2010 Wales, United Kingdom South Wales Valleys Likely cooling towers 22 2 9% Thought to be cooling towers in local industry.[18]
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.[19]
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.[20] 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.[21]
2012 Edinburgh, Scotland, UK 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.[22]
2012 Chicago, Illinois 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.[23]
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.[24]
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.[25]
2012 Pittsburgh, Pennsylvania Veteran's Administration Hospital unknown 22 6 27% 2012 Pittsburgh legionellosis outbreak[26][27][28]
2014 Portugal 2014 Legionella outbreak in Portugal Unknown 375 12 3.2% A widespread outbreak in Vila Franca de Xira district, Portugal.[29]
2015 Bronx, New York Co-op City Co-Op City Cooling Towers 12 0 0.0% 12 people sickened in January 2015. No fatalities reported.[30]
2015 Bronx, New York South Bronx Lincoln Hospital and Concourse Plaza Cooling Towers 113 12 10.6% This ongoing outbreak is currently being investigated by the New York City Health Department[31][32] Out of 17 buildings with cooling towers, five tested positive to the disease, including cooling towers in the Concourse Plaza Hotel and Lincoln Hospital.[33] The Opera House Hotel in the South Bronx is also considered a source of the outbreak.[34]
2015 Bronx, New York Morris Park Unknown 15 1 6.6% The outbreak is currently being investigated by the New York City Health Department[35][36] "Environmentalists sampled 35 cooling towers in the Morris Park area, and 15 came back with positive results."[37]
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 Veterans home Unknown 54 12 27.7% The outbreak investigation is ongoing[38][39]
2015 Bartlett, Illinois Eastview Middle School cooling tower outside of school 1 0 The bacteria was found during an annual inspection of the cooling towers at Eastview Middle School. The school was evacuated on September 23, 2015. Eastview was also closed on September 24 and 25 2015 for cleaning purposes [40] [41]
2014–2015 Genesee County, Michigan Countywide McLaren Regional Medical Center 87 10 8.7% McLaren and the Michigan Department of Environmental Quality is being sued for $100 million in regards to the outbreak.[42] See also Flint water crisis#Possible link to Legionnaires' disease spike.
2016 Sydney, Australia Town Hall, CBD Suspected cooling tower at least 4 0 [43]

Governmental controls to prevent outbreaks[edit]

Regulations and ordinances[edit]

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.[44] 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.[45]

The City of Garland, Texas requires yearly testing for legionella bacteria at cooling towers at apartment buildings.[46]

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.[47]

The Texas Department of State Health Services has provided guidelines for hospitals to detect and prevent the spread of nosocomial infection due to legionella.[48] The European Working Group for Legionella Infections (EWGLI)[49] 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[50] 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.

Many other governmental agencies, cooling tower manufacturers, and industrial trade organizations have developed design and maintenance guidelines for preventing or controlling the growth of Legionella in cooling towers. However, in the US, there are no regulations requiring testing or maintaining any specified levels in these facilities.

Eliminating breeding grounds[edit]

The bacteria grow best in warm water, like the kind found in hot tubs, cooling towers, hot water tanks, large plumbing systems, or parts of the air-conditioning systems of large buildings. Indoor ornamental fountains have been confirmed as a cause of Legionnaires' disease outbreaks, in which submerged lighting as a heat source was attributed to the outbreak in all documented cases.[citation needed] Controlling the growth of Legionella in ornamental fountains is touched on in many of the listed guidelines. However, specific guidelines for solar water heating systems [51]

Adding an antibacterial agent to the automobiles' windshield system's reservoir is also recommended Legionellae have been discovered in up to 40% of freshwater environments and have been in up to 80% of freshwater sites by PCR hybridization assay.

Legionella bacteria themselves can be inactivated by UV light. However, Legionella bacteria that grow and reproduce in amoebae or that are sheltered in corrosion particles cannot be killed by UV light alone.

Legionella will grow in water at temperatures from 20 to 50 °C (68 to 122 °F). However, the bacteria reproduce at the greatest rate in stagnant water at temperatures of 35 to 46 °C (95 to 115 °F).

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.[52] Additional studies indicate ionization is superior to thermal eradication.[53]

A 2011 study by Lin, Stout and Yu[54][55] found Copper-Silver ionization to be the only Legionella control technology which has been validated through a 4-step scientific approach.

A recent research study provided evidence that Legionella pneumophila, the causative agent of Legionnaires' disease, can travel airborne at least 6 km from its source. In 2000, ASHRAE issued guidelines to maintain water systems and to decrease the chances of Legionnaires' disease transmission. The guidelines were not valued because legionella multiply in such temperatures. On the other hand, a lot of states had regulations that limited temperatures in health care facilities in order to reduce scalding injuries.

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.[56]

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. "...[57]

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.[58]

Temperature affects the survival of Legionella as follows:[59]

  • 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.[60][61]

See also[edit]


  1. ^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9. 
  2. ^ Swanson M, Heuner K (2008). Legionella: Molecular Microbiology. Caister Academic Pr. ISBN 1-904455-26-3. 
  3. ^ Archived from the original on November 13, 2014. Retrieved February 4, 2016.  Missing or empty |title= (help)
  4. ^ "Timeline: legionnaires' disease outbreaks in Britain". Telegraph Media Group Limited. Retrieved 31 July 2015. 
  5. ^ McDade J.E.; Brenner D.J.; Boeman F.M. (1979). "Legionnaires' disease bacterium isolated in 1947". Ann Intern Med. 90: 659–661. doi:10.7326/0003-4819-90-4-659. PMID 373548. 
  6. ^ Fraser D.W.; Tsai T; Orenstein W.; et al. (1977). "Legionnaires' disease: description of an epidemic of pneumonia". New England Journal of Medicine. 297: 1186–1196. 
  7. ^ Tsai, TF. "Legionnaires' disease: clinical features of the epidemic in Philadelphia.". Ann Intern Med. 90: 509–17. doi:10.7326/0003-4819-90-4-509. PMID 434627. 
  8. ^ a b c d e f g h i j k Broadbent, C. (1996). Guidance for the Control of Legionella: Water Series No. 1. National Environmental Health Forum Monographs.
  9. ^ "The Westfriese Flora flower exhibition and fair". Retrieved 2010-09-11. 
  10. ^ "25 februari 1999: Legionellabesmetting Westfriese Flora, Bovenkarspel" (in Dutch). Zwaailichten disaster website. 2005. Retrieved December 2, 2011. 
  11. ^ Greig JE, Carnie JA, Tallis GF, et al. (June 2004). "An outbreak of Legionnaires' disease at the Melbourne Aquarium, April 2000: investigation and case-control studies". Med. J. Aust. 180 (11): 566–72. PMID 15174987. 
  12. ^ "Legionella pneumophila cases" (PDF). Retrieved 2015-08-30. 
  13. ^ "Download Menu". Retrieved 2010-09-11. 
  14. ^ "legionnaires disease, Barrow-in-Furness". Archived from the original on 2002-08-16. Retrieved 2013-08-30. 
  15. ^ [1] Archived August 29, 2008, at the Wayback Machine.
  16. ^ "Legionnaires' Disease". Toronto Public Health. 
  17. ^ "Second patient with Legionnaires' disease dies at New Brunswick hospital". The Star-Ledger. September 24, 2008. Retrieved 2011-10-08. 
  18. ^ "South Wales legionnaires' disease outbreak declared over". NHS Wales. 12 October 2010. Retrieved 6 June 2012. 
  19. ^ "DRSP - Direction régionale de santé publique de la Capitale-Nationale" (in French). September 12, 2012. Archived from the original on 2012-10-17. Retrieved 2013-08-30. 
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  22. ^ "Legionnaires' Disease outbreak: Third death reported". 3 July 2012. Retrieved 3 July 2012. 
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  25. ^ "Stoke-on-Trent Legionnaires' source 'could be hot tub'". [The Press]. July 31, 2012. Retrieved 2012-08-02. 
  26. ^ Pittsburgh Veteran's Administration Hospital water contamination investigation ongoing
  27. ^ Noah Brode. "Investigation Reveals Failures of Pittsburgh VA Hospital in Legionnaires' Outbreak". 
  28. ^ "Families of Legionnaires' victims outraged by report on VA outbreak". Pittsburgh Post-Gazette. 
  29. ^ "Extinto o surto de legionella". (in Portuguese). November 21, 2014. Retrieved November 23, 2014. 
  30. ^ "Co-op City towers contaminated with Legionnaires' Disease". NY Daily News. 2015-01-13. Retrieved 2015-08-29. 
  31. ^ "Legionnaires' Disease Bacteria Found in A/C on Bronx Hospital, Mayor says". DNAinfo New York. 
  32. ^ David Shortell, CNN (2 August 2015). "There have been 65 cases since mid-July -". CNN. 
  33. ^ "City confirms 71 cases of Legionnaire's Disease". 
  34. ^ "Hotel that enlivened the Bronx is now a 'hot spot' for Legionnaire's". 
  35. ^ "Health Department Investigating Cluster of Legionnaires' Disease in Morris Park Section of the Bronx" (Press release). City of New York. September 28, 2015. Retrieved September 30, 2015. 
  36. ^ "Legionnaires' Disease". Department of Health and Mental Hygiene. City of New York. Retrieved October 6, 2015. 
  37. ^ Campanile, Carl (September 30, 2015). "Latest Bronx Legionnaires' disease outbreak turns fatal". New York Post. Retrieved September 30, 2015. 
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  42. ^ John Wisely & Jennifer Dixon, Fieger files $100-million suit over Flint Legionnaires' disease cases, Detroit Free Press (February 2, 2016).
  43. ^ "Town Hall area cooling tower suspected after four men contract Legionnaires disease". The Sydney Morning Herald. Retrieved 2016-03-10. 
  44. ^ UK: Health and Safety Executive Microbiological monitoring (weekly dip slide)
  45. ^ "WRAS Home" (PDF). 
  46. ^ "The Dallas Morning News, Garland tough on bacteria". 2007-02-01. Retrieved 2010-09-11. 
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  48. ^ Report of the Texas Legionnaires' Disease Task Force, Texas Department of State Health Services
  49. ^ "European Working Group for ''Legionella'' Infections". Retrieved 2010-09-11. 
  50. ^ Archived from the original on July 6, 2011. Retrieved August 6, 2013.  Missing or empty |title= (help)
  51. ^ "WRAS Home" (PDF). Retrieved 2015-08-29. 
  52. ^ Stout & Yu 2003 "(1) Demonstrated efficacy of Legionella eradication in vitro using laboratory assays, (2) anecdotal experiences in preventing legionnaires' disease in individual hospitals, (3) controlled studies in individual hospitals, and (4) validation in confirmatory reports from multiple hospitals during a prolonged time."
  53. ^ Block 2001.
  54. ^ Lin, Stout & Yu 2011.
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  56. ^ "Long-range transmission of Legionella". Nature Reviews Microbiology. 4 (3): 171–2. March 2006. doi:10.1038/nrmicro1368. 
  57. ^ Nygård K; Werner-Johansen Ø; Rønsen S (January 2008). "An outbreak of legionnaires disease caused by long-distance spread from an industrial air scrubber in Sarpsborg, Norway". Clin. Infect. Dis. 46 (1): 61–9. doi:10.1086/524016. PMID 18171215. 
  58. ^ Wilkinson, Emma (2010-06-13). "Windscreen water infection risk". BBC News. Retrieved 2010-09-11. 
  59. ^ "What is Legionnaires' disease?". Retrieved 2010-09-11. 
  60. ^ Potera C (1998). "Studying slime". Environ Health Perspect. 106: A604–6. doi:10.1289/ehp.98106a604. PMC 1533243Freely accessible. PMID 9831548. 
  61. ^ "An Introduction to Biofilms". Retrieved 2010-09-11. 

External links[edit]