Legionella is a disease-causing bacteria that occurs naturally in water. Each year, thousands of Americans fall ill from contaminated water in public spaces, their places of work, and even their own homes. When multiple individuals contract Legionnaires' Disease from a single source, it is deemed an outbreak.
Scroll through the timeline below to discover all major Legionnaires' outbreaks in the U.S.
This outbreak has affected patients of the University of Wisconsin Hospital. Testing indicated that the Legionella bacteria likely originated in the facility’s hot water systems. The hospital has since taken steps to disinfect its water systems and will continue to do so until the bacteria is eliminated.
Two cases of Legionnaires’ have been connected to the Marriott West Hotel in St. Louis County. The hotel was shut down and its water systems were disinfected after testing indicated the presence of Legionella bacteria. The hotel has since reopened.
Three cases of Legionnaires’ have been connected to the Harrah’s Cherokee Casino Resort. Guest have been notified and the resorts water systems have been treated as a precaution as health officials continue to investigate the exact source.
This outbreak has affected residents of the McHenry Villa senior living community, outside of Chicago. Illinois health officials continue to investigate the outbreak, though the facility’s management team denies that the cases could have originated from the community's water systems.
The investigation into this outbreak have not yet found commonalities between the four cases. As a precaution, some spaces such as a local raceway were temporarily closed.
This outbreak has affected residents of the Warren Barr rehabilitation center. The exact source of the contamination in the facility’s water system is under investigation. The facility has since informed residents and their families, restricted it’s potable water and began using bottled water.
This outbreak affected inmates of the jail complex on Rikers Island. City officials have tested the jail’s water systems and the facility has made modifications to reduce the amount of water vapor, which can carry the Legionella bacteria.
The source of this outbreak is still under investigation. The water systems of multiple locations, including a local church, are being tested as health officials work to identify links between the infected individuals.
NYC health officials tested 20 cooling towers in the area in response to this outbreak. Results indicated that the outbreak most likely originated from the same Upper Manhattan housing complex as another outbreak months before. The cooling tower was shut down and will be disinfected before reactivation.
This outbreak affected residents and those who have traveled to the area. The exact source of the bacteria remains unknown as officials from the State Health Department continue to investigate.
The outbreak is believed to have originated from a particular street in the city. The hot tubs of two hotels in the area were closed as a precaution, but the exact source of the bacteria remains unknown as officials continue to investigate.
The NYC Health Department immediately tested 20 cooling towers in the area for Legionella bacteria and found that the bacteria originated from a water cooling tower in an Upper Manhattan housing complex.2018
The outbreak was traced to the Disneyland amusement park in Orange County. Disneyland staff identified two cooling towers in the park with elevated levels of Legionella bacteria. The towers were thoroughly cleaned and then shut down.
The outbreak was traced to the SpringHill Suites hotel, which was forced to close and was thoroughly cleaned before reopening more than a week later. The director of the Williamson County Health District attributed the outbreak to improper maintenance of the hotel’s water systems.
The outbreak was traced to the Rio Hotel and Casino. While there were only seven confirmed cases linked to the Rio Hotel, the Southern Nevada Health District suspects that as many as 29 cases of Legionnaires’ and 56 cases of Pontiac fever, a milder illness caused by the same bacteria, could have originated from the Rio. Despite multiple attempts at disinfection, the hotel’s water systems were not free of the bacteria until November of that year.
The NYC Health Department determined the outbreaks were likely caused by mist from one or more contaminated cooling towers. All 116 cooling towers in Lenox Hill were tested for Legionella bacteria. Of those, 42 tested positive, and 24 had levels high enough to be potentially dangerous to humans. While the Health Department was unable to determine exactly which tower was the source of the outbreak, all were thoroughly cleaned and disinfected.2017
Officials tested 35 cooling towers in the area. Of those, 15 tested positive for Legionella bacteria. These included several at Lehman High School, the Albert Einstein College of Medicine, and the Bronx Psychiatric Center. The contaminated towers were later disinfected.
The outbreak affected residents of the Illinois Veterans Home. All water systems in the home were shut down. Bottled water was used for cooking, drinking, and bathing while the water systems were tested and cleaned. Health professionals from the Adams County Health Department, Illinois Department of Public Health, and even the federal Centers for Disease Control and Prevention spent more than a week at the facility to manage the outbreak.
Upon testing, 12 buildings in the area were found to have Legionella bacteria, including Lincoln Hospital and the Concourse Plaza Mall. This outbreak remains the worst in New York City history, and encouraged New York lawmakers to take legislative action. This legislation would become Local Law 77, which would later be adopted and enacted by the New York State government.2015
The outbreak affected residents and guests of the Co-Op City development of the borough. Testing revealed that a cooling tower in the complex had been contaminated with Legionella bacteria. Riverbay Corporation, the property management company that manages Co-Op City, was reported to have paid $200,000 to disinfect the complex.
The exact cause of the outbreak is unknown. However, experts believe it was likely a result of contaminated water, as the outbreak began when the county switched its water system to draw from the Flint River, and ended when it switched back to Detroit’s system.2014
The outbreak affected residents of the Wesley Ridge Retirement Community. An investigation by the Centers for Disease Control and Prevention (CDC) revealed that one of the facility’s cooling towers contained elevated levels of Legionella bacteria.2013
This outbreak affected guests and visitors of the JW Marriott Hotel in Chicago. An investigation determined that the Legionella bacteria originated from a decorative fountain in the lobby of the hotel, which had not been properly treated.2012
This outbreak affected residents of the VA Pittsburgh Healthcare System. The CDC determined that the hospital’s water systems had not been properly maintained. An investigation later determined that hospital staff knew about the presence of Legionella bacteria in the water more than a year before the outbreak, yet did not warn patients. In 2013, VA officials were required to testify before the U.S. Congress as to why the situation was handled so poorly.2011
This outbreak affected patients admitted to an oncology wing of New Jersey’s St. Peter’s University Hospital. Tests later indicated that chlorine levels in its water system had not been properly tested and were allowed to drop too low.2008
This outbreak was traced to the Casa Del Rey restaurant in Rapid City. Tests indicated that a decorative fountain in the restaurant had dangerously high levels of Legionella bacteria. The restaurant removed the fountain soon thereafter.
This outbreak affected patients at the Sound Shore Medical Center. Tests indicated an outdoor cooling tower was the source of the Legionella bacteria. It was immediately shut down and disinfected.
This outbreak affected guests of an Ocean City hotel. Testing suggested the Legionella bacteria originated from its potable water system. The hotel superheated its water system, replaced showerheads and faucets in rooms where the victims had stayed, and disinfected the remaining ones.
TInvestigation into this outbreak at a Waterbury office complex suggested the Legionella bacteria originated in three contaminated cooling towers.2005
This outbreak affected workers at an automotive engine manufacturing plant outside of Cleveland. The plant was forced to close for several days while all water systems were tested and disinfected.2001
This outbreak was traced to a whirlpool spa near an Atlanta hotel’s swimming pool.
This outbreak affected patients of the Harford Memorial Hospital in Havre de Grace. The source of the outbreak is believed to have been a contaminated hot water tank.
This outbreak affected workers at a local postal facility. Its exact cause is unclear, though a water cooler was removed from the facility.1999
This outbreak was traced to a Lowe’s Home Improvement warehouse in Christiansburg, where one of the whirlpool hot tubs on display was contaminated with Legionella bacteria. In response, Lowe’s drained and disinfected all whirlpool hot tubs displayed in all of their locations.1996
This outbreak affected patients of a small hospital in rural Pennsylvania, 60 miles outside of Harrisburg. Officials indicated that its most likely source was the hospital’s cooling tower, the largest in the area. It was immediately sanitized.1995
This outbreak was traced to a local hospital. An investigation suggested its cooling towers were the source of the Legionella bacteria.1994
This outbreak was linked to a number of cooling towers in the area with dangerous levels of Legionella bacteria. All were decontaminated, though it was unclear which were responsible for the outbreak. No new cases were reported following decontamination.
This outbreak affected inmates and one employee of a Michigan prison. Two of its cooling towers were contaminated with Legionella bacteria. Both were shut down and decontaminated.
Ten cooling towers and one decorative fountain in downtown Providence were contaminated with Legionella bacteria. All were later decontaminated.
This outbreak was traced to a decorative fountain in a hotel lobby, which had been contaminated with Legionella bacteria.1993
This outbreak, which was relatively large for the size of the community, most likely originated from a local grocery store’s misters used to spray water on produce. These were later removed.
This outbreak affected attendees of a high school reunion held at the Cow Palace Inn in Lamar. It closed, and disinfected all ventilation, heating and water systems.1989
This outbreak is believed to have originated from local cooling towers.
This outbreak affected patients at the City of Hope Hospital and was traced to a contaminated cooling tower. The affected wing was evacuated and all water systems were purged and disinfected.
The cause of this outbreak is believed to have been contaminated water at a construction site near a grocery store in rural Maryland. As construction continued for weeks before the outbreak was traced to the site, health officials were unable to take proper samples.1986
This outbreak affected the patients of a Rhode Island hospital. Its cause was originally believed to have been contaminated potable water. Later tests indicated cooling towers contaminated with Legionella bacteria were to blame.1983
This outbreak affected patients of a hospital in Upstate New York. Testing confirmed its hot water system had been contaminated with Legionella bacteria, and that patients likely became infected through showering.1982
The source of this outbreak has not yet been determined.1981
This outbreak affected tenants and employees working in an office building in San Francisco. The source is believed to have been a nearby cooling tower that had become contaminated with Legionella bacteria.
This outbreak affected patients of a local hospital, as well as residents of the local community. Though its source was not definitively determined, its impact on residents of the community living downwind from the hospital suggests the Legionella bacteria originated in one of its cooling towers.1980
This outbreak was traced to a contaminated cooling tower at a Holiday Inn in Eau Claire.
This outbreak was traced to one or more water evaporative condensers in the clubhouse of an Atlanta country club.
All victims were patients of the Wadsworth Medical Center outside of Los Angeles.
This outbreak affected individuals who had visited or stayed at the Indiana Memorial Union Hotel in Bloomington. Though the hotel’s cooling tower is believed to be one source, it was likely not the only one, as an additional individual in Bloomington became infected in the weeks after the hotel’s water systems were cleaned.1979
This outbreak affected patients, staff, visitors and passersby of a local hospital. The source is believed to have been a contaminated auxiliary cooling tower.1978
This outbreak affected patients of a local hospital. Its source was never determined.
This outbreak took place across the state during a three-month period. Its source remains unknown.
The source of this outbreak remains unknown.1977
In late July, more than 4,000 members of the American Legion, an organization of U.S. war veterans, gathered at the Bellevue-Stratford Hotel in Philadelphia for its yearly convention. The four-day celebration ended without incident, and its members, called Legionnaires, returned home.
In the days following the convention, many of these veterans began to fall ill with pneumonia-like symptoms. By August 2, 22 people were dead and the medical community was facing a historic crisis. As people who had attended the convention continued falling ill and as the death toll continued to climb, the public was growing concerned. Scientists at the CDC were unable to identify what exactly was causing the fatal disease.
Theories about the disease swirled. Was it a new form of influenza? A biological attack? By the time CDC microbiologist Dr. Joseph McDade isolated the bacteria causing the disease, the outbreak had already run its course. In total, there had been 221 confirmed cases and 34 fatalities.
The bacteria were named Legionella pneumophila, and the disease it caused was dubbed Legionnaires’ Disease after the group it had so badly affected.
Once the disease had been officially identified, it became evident Legionnaires’ Disease was nothing new, and that the Philadelphia outbreak of 1976 was not the first time groups of people had been infected.
Perhaps it is not surprising that the Bellevue-Stratford Hotel, which had been the source of the major outbreak that led to the identification and naming of Legionnaires’ Disease, was also the site of another outbreak, just two years earlier. Members of the Independent Order of Odd Fellows, a fraternal organization, had fallen ill after the hotel had hosted their yearly convention. It is believed the outbreak was caused by the same contamination in the air conditioning system that would later cause the 1976 outbreak.1974
A severe outbreak of a mysterious illness at St. Elizabeth’s Hospital, once known as “St. Elizabeth’s Fever” is now recognized as Legionnaires’ Disease.1965
Affecting employees of the Hormel Food Corporation office, this is the earliest confirmed outbreak of Legionnaires’ Disease within the United States.1957