Legionellosis epidemiology and demographics

Infection in the U.S.:
Each year, between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the U.S. However, many infections are not diagnosed or reported, so this number may be higher. More illness is usually found in the summer and early fall, but it can happen any time of year.

LD is a reportable condition in most states; because of under-diagnosis and underreporting, however, only 2%-10% of estimated cases are reported.

Worldwide infection:
Below is a list of Legionnaires' disease outbreaks, followed by a discussion of many of them:

Philadelphia, 1976
The first recognized outbreak occurred on July 27, 1976 at Bellevue Stratford Hotel in Philadelphia, Pennsylvania, where members of the American Legion, a United States military veterans association, had gathered for the American Bicentennial. Within two days of the event’s start, veterans began falling ill with a then-unidentified pneumonia. Numbers differ, but perhaps as many as 221 people were given medical treatment and 34 deaths occurred. At the time, the U.S. was debating the risk of a possible swine flu epidemic, and this incident prompted the passage of a national swine flu vaccination program. That cause was ruled out, and research continued for months, with various theories discussed in scientific and mass media that ranged from toxic chemicals to terrorism (domestic or foreign) aimed at the veterans. The U.S. Centers for Disease Control and Prevention mounted an unprecedented investigation and by September, the focus had shifted from outside causes, such as a disease carrier, to the hotel environment itself. In January 1977, the Legionellosis bacterium was finally identified and isolated, and found to be breeding in the cooling tower of the hotel’s air conditioning system, which then spread it through the entire building. This finding prompted new regulations worldwide for climate control systems.

Some do not believe that the air conditioning was conclusively proven to be the cause of the outbreak. According to Dr. Victor L. Yu, chief of the infectious disease section at the Oakland Veterans Affairs Medical Center in Pittsburgh, researchers still haven’t identified the exact source. Morbidity and Mortality Weekly Report (MMWR), a weekly publication of the US Centers for Disease Control and Prevention (CDC), stated in 1977 that no source was found in this first outbreak of Legionnaires' disease at the Bellevue Stratford Hotel.

United Kingdom, 1985
A large outbreak of Legionnaires' disease was associated with Stafford District General Hospital. A total of 68 confirmed cases were treated in hospital and 22 of these patients died. A further 35 patients, 14 of whom were treated at home, were suspected cases of Legionnaires' disease. All these patients had visited the hospital during April 1985. The BBC reported these statistics as 101 infected with 28 deaths resulting.

Netherlands, 1999
In March 1999, an outbreak in the Netherlands occurred during a flower exhibition in Bovenkarspel. 200 people became ill and at least 32 people died. There is a possibility that more people died from it, but these people were buried before the Legionella infection was recognized. The source of the bacteria were probably a whirlpool and a humidifier in the exhibition area.

Spain, 2001
The world’s largest outbreak of Legionnaires' disease happened in July 2001 (patients began 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%).

A controlled case study matching 85 patients living outside the city of Murcia with two controls each was undertaken to identify the outbreak source; the epidemiologic investigation implicated the cooling towers at a city hospital (Morales Meseguer Hospital). An environmental isolate from these towers with an identical molecular pattern as the clinical isolates was subsequently identified and supported that epidemiologic conclusion.

Norway, 2001
The first known case of the disease in Norway occurred in 2001 when 28 people were infected in the city of Stavanger, and seven died. At first the authorities were puzzled as several of the victims lived in other locations, including one in Germany and another in England. After a massive investigation a fountain in the small lake of Breiavatnet was suspected as the source of the outbreak. But the fountain had not sprayed the bacteria into the air, the source was a cooling tower at the nearby SAS Radisson hotel. Only three of the infected had stayed at the hotel, but the exit vent of the cooling tower was at ground level next to a public bus stop, explaining the other victims.

United Kingdom, 2002
In 2002, Barrow-in-Furness suffered the U.K.’s worst 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.

France, 2004
Researchers found that the Legionnaires' disease bacteria spread through the air up to 6 kilometers from a large contaminated cooling tower at a petrochemical plant in Pas-de-Calais in northern France. That outbreak killed 21 of the 86 people with laboratory-confirmed infection.

Norway, 2005
In May 2005 there was a second&mdash;greater&mdash;outbreak in Norway, this time originating in the southeastern town of Fredrikstad. As of 8 June 2005, 52 patients were confirmed infected and ten people were dead. The dead were all from Fredrikstad or nearby cities, in age ranging from 68 to early 90's. The source of the outbreak unexpectedly came from an air scrubber (an industrial air purification facility; this particular one operated by Borregaard Industries in Sarpsborg). Such an installation has never before been reported as a source of Legionellosis anywhere in the world. Although the source was finally identified by DNA matching, it was also fairly well identified by analysing risk increases from people living near suspected sources.

New Zealand, 2005
An outbreak of Legionnaire's disease hit the New Zealand city of Christchurch in mid-2005, with 20 reported cases (three fatal) between late April and August. A cooling tower at the city's Ravensdown Fertiliser Plant was implicated in the outbreak. The outbreak led to plans by the city council to create a registry of all air-conditioning cooling towers within the city.

Toronto, 2005
In October 2005 at least 21 people died and over 100 fell ill during an outbreak at the Seven Oaks Home for the Aged in Toronto, Ontario, Canada. Legionnaire’s disease was originally ruled out as being the cause, but post-mortem examinations confirmed that victims had Legionella bacteria in their lungs. The outbreak is still being investigated, and researchers believe this particular outbreak may be related to a new strain of the bacteria.

Australia, 2007
The outbreak is believed to have started during New Year's Eve celebrations at Circular Quay, on Sydney's harbour. Thought to have started from a cooling tower (where 1,400 cfu/ml Legionella was found) from an adjacent office building, four cases were initially confirmed, but there were concerns due to the fact that Circular Quay is one of the most populated areas in Sydney on New Year's Eve. As a result, there could have been potentially many more cases. On Saturday, January 20 the NSW Health Authority reported that three more cases had developed overnight, bringing the total reported cases to 7.

New York 2007
An outbreak of Legionnaire's disease occurred in Long Island, New York. It was believed to have started on September 27, 2007. It occurred in 2 separate nursing homes. 3 people have already died as of 9/27/07.