A Base Guideline For Cooling Towers


Consider cleaning and disinfecting cooling towers or altering the water treatment regimen if a case of Legionellosis is confirmed.


Keeping Legionella levels below detectable levels in cooling towers is nearly impossible. Low levels such as 1 cfu/ml however are not thought to present a significant risk. The level of 10 cfu/ml, thought arbitrary, seems an appropriate action level for hospitals that treat high-risk patients.

Wales’ largest outbreak, Sept. 2010


As of September 23, officials from the Health and Safety Executive (HSE), Public Health Wales (PHW), and eight South Wales localities had not been able to pinpoint the source of Legionella that caused 22 cases of Legionnaires’ disease. Two people have died, a 64-year old woman and a 74-year old man. Having identified no single building visited by all the people who became ill, the investigators are focusing on cooling towers.

Hotel in Dubai, 3 cases, 1 death, Jan. 2009


A 69-year-old British broadcaster died on 29 January after contracting Legionnaires’ disease. The man stayed at a 5-star hotel in Dubai in mid-January and returned to the UK on 20 January. Two other guests of the same hotel contracted the disease and recovered.

Hospital in Ohio, March 2011


Test results show the hot water system in the Hospital’s new addition contained Legionella bacteria, increasing the likelihood that contaminated water there had a role in an outbreak of Legionnaires’ disease that sickened 11 hospital patients. Source Dayton Daily News: March 14, 2011.

Germany’s largest outbreak, Dec. 2009


Around the end of 2009, approximately 65 German residents ranging from 27 to 96 years of age contracted Legionnaires’ disease, five of whom died. Nearly all of them lived or worked in Ulm or Neu-Ulm, in southwest Germany. The investigators suspected a cooling tower was the source of contamination even though the outbreak occurred in winter.

Known Outbreaks - Reported Outbreaks

Across the Globe

Oneida County, NY, 7 cases, July-Sept. 2008


The Oneida County Health Department has not identified a common link for seven cases of Legionnaires’ disease that occurred in the Upstate New York county from July through October 3rd. All seven have recovered. Sources: uticaod.com and romesentinel.com

Hospital, Atlanta (USA), 4 Cases, Jan. 2009


A State of Georgia epidemiologist said that four patients diagnosed with Legionnaires’ disease in January appear to have contracted the disease during their stay at Atlanta’s largest hospital. The hospital reported that all four patients were responding well to antibiotics. Legionella was found in water samples collected from rooms on the hospital floors where the four patients had stayed. The hospital closed those floors until water samples tested negative for Legionella following chlorination procedures.

Norway, 5 Cases, 2 Deaths, July 2008


Eastern Norway experienced an outbreak of Legionnaire’s disease in five people from mid-June to late July, two of whom have died.

Los Angeles, California, March 2011


Four Swedish men who attended an event at private club where Legionairres disease was diagnosed. Legionairres disease or Pontiac Fever, a milder form of Legionnaires disease caused by bacteria that thrives in warm air-conditioning systems. At the time health officials said it the illness may have been spread by a fog machine used at the party. 

Syracuse, NY, 13 Cases, 1 Death, July 2008


An outbreak of Legionnaires’ disease, beginning on June 30, in the Onondaga Hill area of Syracuse resulted in 13 infected persons, of whom six were patients at a hospital and one a resident of a nursing home. One of the infected persons has died.

A Base Guideline for Domestic Water Systems


Consider disinfecting the domestic water system if:
(1) 30% or more of samples taken in any given screening test positive for Legionella
(2) One or more samples in a screening, but fewer than 30%, test positive and the hospital has had prior cases of nosocomial Legionellosis
(3) A case of nosocomial Legionellosis is confirmed.


Before applying the above guideline to a specific situation you must understand that the 30% figure is arbitrary. It has been reported that nosocomial Legionellosis occurred when Legionella were recovered from 30% or more of selected water outlets, disease can occur and has occurred when fewer than 30% of the samples in a given screening test positive. This is the case in high-risk patient areas or high concentrations of Legionella. Concentration is a key factor as well. There are no standard action levels for water sample results because the level above which domestic water systems or cooling towers should be disinfected, and below which occupants are considered safe will depend on the building population. In high risk patient areas, any positive sample is a matter of concern, even if the Legionella count is very low. However, in areas with a population of low risk patients, samples with a low Legionella count may not represent a high enough risk to warrant disinfection. Although the risk of higher concentrations can develop if the necessary precautions are not taken.


The term “disinfect” isn’t also a general term. The best corrective action to take will vary from situation to situation so no definite way to disinfect can be given without the help of a consultant.

Determining when to Disinfect Systems


Many factors need to be considered before deciding whether or not to take corrective action and if so, what action to take. No set of guidelines apply to every facility all the time. However, a basic guideline is useful as a starting point for decision making.

Las Vegas resort, August-Oct. 2008


Health officials said two guests of a Las Vegas resort were diagnosed with Legionnaires’ disease in 2007 and another two in the past two months. All four have recovered. The same resort was associated with an outbreak of Legionnaires’ disease in 2001. Source: Review-Journal and AP

Wisconsin Hospital Water Wall in March, health officials blamed a water wall at a hospital in Wisconsin for eight cases of Legionnaires’ disease. The hospital turned off the water wall with no plans to restart it.

Legionnaires’ Disease cases among fans at world handball championships, Croatia, Feb. 2009


Four Norwegians, one Danish, one Swede, one Croat and about twelve Serbians who attended the World Handball Championships in Croatia contracted Legionnaires’ disease. Preliminary epidemiologic evidence indicated that the source of the illness was probably in the sports halls rather than in the hotels where the fans were staying. None of the players became ill with the disease.

11 infant cases and 3 deaths, Cyprus hospital, Dec. 2008


Eleven infants born between December 18 and 22 at a private hospital in Cyprus contracted Legionnaires’ disease. The babies were discharged from the private hospital in good condition but then admitted to the intensive care unit of another hospital between December 25 and 29 because of Legionnaires’ symptoms. Three of the children have died. As of January 20th, one of the babies was still in the hospital, not yet able to breath on its own. The other seven have been treated and released. Reports indicate that portable ultrasonic humidifiers were the source. The maternity ward and nursery were closed on December 29th, immediately following laboratory confirmation of the first cases.

Ron George CPD, President, Plumb Tech LLC


With 35 years of experience designing plumbing and mechanical systems for several major architectural, engineering, and design & construct firms. He has designed plumbing, mechanical, and fire protection systems for all building types including airports, stadiums, industrial manufacturing facilities, office buildings, commercial and retail buildings, hospitals, laboratories, prisons, jails, hotels, apartment buildings, military projects, high rise and educational facilities.

US military base in Michigan, 6 cases, Aug. 2010


Legionnaires’ disease has been identified in six civilians who worked at or had visited an Air National Guard base in Michigan. The first three cases were diagnosed in late July. The sixth case was diagnosed on August 4th. Workers were moved out of the buildings believed to have been associated with the cases until the water was disinfected and tested, according to Army health command leaders. In July, A bacterial outbreak at the same base sickened more than 30 people. Source: news media.

Whirlpool spa in France, 3 cases, 1 death, May 2010


French investigators identified a public whirlpool spa as the most probable source of three LD cases that were confirmed in May. The first case involved a woman in her early 70s who used a sauna located in the room with the whirlpool spa in late April, but did not use the spa. She developed LD symptoms three days later, was hospitalized, and survived after antibiotic treatment. Another woman visited the spa six days after the first case did and was in the room with the whirlpool. She was diagnosed by urinary antigen and died just a few days later despite intensive antibiotic treatment. She was in her early 50s. The third case, a man in his early 30s, visited the spa 17 days after Case 1 did. He used the whirlpool spa and was diagnosed with LD and hospitalized. He recovered after antibiotic treatment. Case 1 had an underlying chronic disease, Case 2 was a smoker, but Case 3 had no risk factors. The whirlpool spa was closed by health authorities three days after notification of the second case. Legionella (150,000 cfu/l Lp1) was found in samples collected from the spa at that time. The Lp1 strains found in the water and in the patients were indistinguishable by monoclonal antibody subtyping, sequence-based typing, and PFGE. Source: Campese C, Roche D, Clément C, Fierobe F, Jarraud S, de Waelle P, Perrin H, Che D. Cluster of Legionnaires´ disease associated with a public whirlpool spa, France, April – May 2010. Source Eurosurveillance Edition 2010: Volume 15/Issue 26, Article 3. Available online.

Water wall, Wisconsin, 8 cases, March 2010

Rochester, NY, Nursing Home, 2 Cases, Sept. 2008


Two residents of an assisted living facility in the Rochester area contracted Legionnaires’ disease. The first case occurred in late August and the second about two weeks later. Source: Rochester Democrat and Chronicle.

Bali vacationers, 2 cases, Aug. 2010


Two Australians who traveled independently to Bali contracted Legionnaires’ disease in August. Both stayed at the same hotel, with overlapping trips between July 29 and August 8.

Scarborough, UK, 3 cases, Sept. 2008


Two residents of Scarborough and a visitor to the area contracted Legionnaires’ disease in September. Two of the three have recovered but the other has died. Investigators could not determine the source of the outbreak.

What to do if there is an Outbreak


The first thing that should be done is to contact the local or state health department. In some cases a government agency, like the Occupational Safety and Health Administration (OSHA), may investigate cases of Legionellosis. However, when the government is unable to help, a private consultant (click here for a consultant) will be needed. If a consultant is needed, the best thing to do is to find a consultant who is knowledgeable in this area.


Being prepared to take action immediately and get outside is crucial. Infection control, facility management, administration and appropriate others should review the 1997 CDC document, Guideline for Prevention of Nosocomial Pneumonia.

A Legionnaires’ disease outbreak was reported at a Hotel in Nevada. It prompted officials to warn guests who stayed that summer that they might be at risk to develop the potentially deadly disease. Health officials confirmed 6 cases among guests. All 6 people were treated and have recovered.  How can hotel guests catch Legionnaire’s? By inhaling legionella bacteria that grows in hot tubs, air conditioners, and decorative fountains. In a letter to guests, the hotel said that it treated the tainted water source and latest tests show no detectible bacteria levels. But those that stayed during the two week period may still be at risk – symptoms can show up as long as 14 days after exposure to bacteria. Who’s most at risk? People with weakened immune systems like the elderly and smokers. Symptoms like headache, muscle pain, chills, and fever present early – but infected people eventually experience a phlegm-heavy cough, chest pain, fatigue, vomiting, diarrhea, and mental changes like confusion. In some cases, Legionnaire’s can result in fatal complications like respiratory and kidney failure, and septic shock. If you think you’ve been exposed to legionella bacteria, see a doctor who can prescribe aggressive antibiotics designed to fight legionella. 

Maryland assisted living facility, 2 cases, Aug. 2010


Two residents of a Maryland (USA) assisted living facility contracted Legionnaire’s disease. Both were hospitalized and recovered. The facility implemented water restrictions on September 2 per the county health department’s recommendation. Source: Washington Post.

Hotel and Casino, July 2011

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