A Legionnaires’ disease outbreak in New York City in the South Bronx has now sickened at least 108 people and 10 people have died from the illness. Health officials said it is the largest known outbreak in New York City.

According to the New York City Department of Health and Mental Hygiene, Legionnaires’ disease cases began to be reported in the South Bronx on July 10. By July 30, Mayor Bill de Blasio’s office reported 46 cases and two deaths.

City officials tested 17 cooling towers in the South Bronx and five were found to be contaminated with Legionella bacteria. The five locations were identified as the Concourse Plaza shopping center, Lincoln Hospital, Opera House Hotel, Streamline Plastic Co., and a Verizon office building. All five systems were disinfected. City health officials stated that they are “confident that one or more of the five locations that tested positive was the source of the outbreak” and epidemiological investigation is ongoing.

Since Legionnaires’ disease has an incubation period of up to 10 days, even though the suspected cooling towers were cleaned, the disease count continued to rise and more cases may still be reported after this issue went to press.


According to the Centers for Disease Control and Prevention (CDC), Legionnaires’ disease is a severe pneumonia caused by a type of bacteria called Legionella. (A milder flu-like form of the disease is called Pontiac fever. The two illnesses are also referred to as legionellosis.) Death can occur in 5-30 percent of Legionnaires’ disease cases.

Legionella bacteria are found naturally in the environment, usually in water. These bacteria grow best in warm water. People can contract Legionnaires’ disease when they breathe in a mist containing the bacteria. The bacteria are not spread person-to-person.

Cooling towers are potential breeding grounds for Legionella bacteria if they are not properly maintained. Water within cooling towers is heated via heat exchange, which is an ideal environment for the heat-loving bacteria to grow. Since heat and evaporated water are rejected out of the top of the tower in the form of a fine cloud-like mist, which can spread nearby, contaminated cooling towers can be a source of Legionnaires’ disease.

At a July 30 press conference, New York City health commissioner, Dr. Mary Basset, noted, “In the United States, and in our city, the number of cases of Legionnaires’ disease has been increasing since the year 2000. The reasons for that are not clear, but may have to do with better case ascertainment. We have better and better lab tests that enable us to make the diagnosis. And it also may have to do with the fact that we have an aging population, more people susceptible to the infection.” According to “Legionellosis on the Rise: A Review of Guidelines for Prevention in the United States,” published in the Journal of Public Health Management & Practice, reported cases of legionellosis more than tripled between 2001 and 2012 in the U.S.

By Aug. 2, it was announced that 71 people had been sickened in New York City and four were dead.


Matt Freije has specialized in Legionella prevention since founding HC Info, San Diego, in 1995. He has written books, developed water management plan templates, taught seminars, and written and narrated e-learning courses. He said, “Legionella bacteria need food and a proper environment for growth.” They need “the right temperature, protection, and nutrients.”

He noted that cooling towers “must be properly treated and maintained to minimize Legionella.” As for recommended control measures, Freije said, “There are a number of specific measures. Most of them fall into one of four categories: cleaning, water treatment, minimizing stagnation, and routine inspections for proper operation of the cooling tower and water treatment system.”


Daniel T. Donnelly, CEO of Donnelly Mechanical, Queens Village, New York, a commercial HVAC and energy services contractor, stated that cooling tower problems can be avoided with “a regimented maintenance program and a regimented water treatment program.”

Donnelly said that in performing maintenance, you need to look at the whole system including the cooling tower, pumps, and automated controls. “In addition to that you have a regular water treatment program.”

His recommendations are that cooling towers “should at least be checked once a week. Someone should be physically looking at it once a week.” He also recommends monthly maintenance; two tower cleanings a year (in the city he does not believe one cleaning is enough); and a comprehensive water treatment program.

Jim Cunningham, New York representative for Nu-Calgon Inc., St. Louis, a supplier of water treatment products, said, “Chemical preventive maintenance is the key to keeping a cooling tower system operating in a clean, safe, and efficient manner. There are many good products and companies available to accomplish this.

“Towers and associated piping and equipment should be physically and chemically cleaned of dirt, sediment, scale, and organic material. There should be an ongoing chemical treatment program using cooling tower biocides/algaecides to prevent all biological growths in the system water. This makes the system inhospitable to a wide range of biological activity, including Legionella. Monthly bacteria testing can be done to ensure control.”

Commenting on frequency of monitoring, Freije said, “Some control measures should be performed daily and others weekly, monthly, or even less frequently. Chemical and microbial tests should be conducted per the water treatment vendor’s recommendations but no less than any frequency recommended by the Cooling Technology Institute (CTI) or ASHRAE. In my opinion, cooling towers should also be tested periodically for Legionella. In its new publication, Recognition, Evaluation, and Control of Legionella in Building Water Systems, the American Industrial Hygiene Association (AIHA) recommends monthly Legionella testing in cooling towers.”

Cunningham said, “For very large systems at hospitals and other commercial buildings, the cooling tower should be visually inspected every day by maintenance staff and some water tests done every day to monitor conditions. Bacteria tests take time. For small and medium size cooling towers, a monthly inspection and testing to confirm control is recommended.”

Regarding how prevalent Legionella are in cooling towers, Cunningham said, “The prevalence of Legionella in cooling towers is unknown since very few systems are ever tested specifically for Legionella. However, biological growths such as bacterial slimes and algae are fairly common in cooling tower systems. The presence of any biological growth is a signal that conditions are ripe for more biological growth and the cooling tower needs to be cleaned and treated.

“Most large cooling tower systems have some kind of chemical water treatment program in place to prevent scale buildup, corrosion, and biological growths,” he noted. “An interruption of treatment or inadequate treatment could lead to an outbreak of biological growths.”

Freije pointed out that ASHRAE’s new Legionella standard, ANSI/ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems, specifies the essential components of a water management plan. To comply with the standard, he said, “building operators must implement a water management plan for cooling towers and other water systems that can harbor and transmit Legionella bacteria. HVAC contractors can play a role in the implementation of a water management plan by providing services related to cooling tower cleaning and maintenance.”


On Aug. 3, Mayor de Blasio said in a statement, “A more systemic solution is required to prevent the cycle of these outbreaks from continuing. This week, new legislation will be announced designed to halt future outbreaks of Legionnaires’, and place new emphasis on long-term prevention. The comprehensive package will address inspections, new recommended action in the case of positive tests, and sanctions for those who fail to comply with new standards.”

The mayor announced in a press conference on Aug. 4 that there were 86 cases of the disease reported and seven deaths. He emphasized, “We’ve been aggressively investigating and testing any and all possible sources of this outbreak.”

At a press conference on Aug. 6, Mayor de Blasio announced a total 100 cases and 10 deaths. He said the city was now issuing a health commissioner’s order that instructs the owners or managers of buildings with cooling towers “to test and disinfect their cooling tower within the next 14 days. Failure to comply with the commissioner’s order is a misdemeanor.”

Also on Aug. 6, New York Gov. Andrew Cuomo announced free Legionella testing for all cooling towers statewide.

Both the city and state were now on full alert, making a concerted effort to halt the outbreak.

On Aug. 7, Dr. Basset issued a statement saying “We now see the frequency of diagnoses decreasing, as well as the number of emergency department visits for pneumonia in the South Bronx. We have fewer new cases, people are seeking care promptly and getting treatment promptly. We’re optimistic that we’ve seen the worst of this outbreak, and that our remediation efforts are having an impact.”

She added, “We must all remain vigilant. The Health Department will continue to monitor for new cases and check that building owners are continuing remediation efforts.”

Publication date: 8/10/2015

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