1976 was a busy year in Philadelphia. They were holding the Bicentennial celebration, commemorating the two-hundredth anniversary of the Declaration of Independence. As part of the year-long festivities, the city had become a hub for events, hosting the championship game of the NCAA Final Four, as well as the all-star games for baseball, basketball and hockey. On the 4th of July, around 2 million people descended on the city for the celebrations, which featured a five hour parade with over 40,000 marchers and floats from every state. But it was to be a small, 2000 person event that would go down in history.
On July 21, 1976, the American Legion opened their annual convention in the Bellevue-Stratford Hotel in Philadelphia with veterans across the country in attendance. However, three days after the convention ended, Legionnaire Ray Brennan, a retired Air Force Captain died at his home from a heart attack. On July 30th, another Legionnaire died of a heart attack and the next day, six more passed away. Within a week, 130 people had been hospitalized and 25 had died. And no one knew why.
Dr. Ernest Campbell, a physician based out of Bloomsberg, Pennsylvania, noticed he was treating three patients for the same conditions: tiredness, lung congestion, and chest pains. In taking their history, he noticed all three had been attendees at the Legionnaires Convention, and told the Pennsylvania Department of Health. Other doctors reported the same, and the investigation began. People who had attended the convention had intense flu-like symptoms if they were lucky. However, the most serious cases had individuals coughing up blood as their lungs flooded. At the same time, officials at the Legion had noticed Legionnaires appearing in the obituaries. The Department of Health obtained lists of attendees and trying to see what they all had in common.
David Fraser was the CDC agent responsible for investigating the outbreak. When investigating an outbreak, one of the first things to do is to ascertain exactly what everyone was doing prior to the disease emerging. This can include what they ate, where they stayed, and who they were with, as these are all mechanisms by which they might have picked up the disease. Individuals like Typhoid Mary are often cited as Patient Zero, as those who come into contact with them can then go on to develop and spread the disease. Or it comes from some other source, like bad food, at which point you can track the disease back to a specific source. After ruling out other causes, Fraser established that the infection was related to the Bellevue Stratford Hotel although he couldn’t establish what exactly had caused it. Tests for all known respiratory infections and toxicological agents came back negative.
The investigation faced two major hurdles. The first was that there was a swine flu outbreak that was occurring at the same time, so investigators had to rule out swine flu as a potential culprit. The second was that while 149 of the infected had been at the Legionnaires convention, another 33 of those infected had not been attending. One notable example was that of a marching bus band driver, who was in town for several hours, and spent most of that on the bus. This led to fear and panic among the public, with people not attending the funerals of those who had this disease. There was even speculation that this was the start of germ or chemical warfare, or even terrorism.
In December of 1976, Joseph McDade identified the bacteria responsible for the outbreak. The CDC published their final report in April 1977, and named the bacteria Legionella pneumophila. We now know that Legionella pneumophila thrives in warm, standing, water, and can be transmitted through water droplets in the air, such as in air-conditioned office buildings. Another way it can spread is when someone chokes during drinking, ingesting or swallowing, as then water is able to enter the lungs. Treatment depends on the severity of the disease, but involves some combination of antibiotics, rehydration if they have diarrhea, and observation for response. If caught early enough, the disease can be completely cured.
However, this is not to say that Legionnella has been eradicated. The ubiquitous nature of air conditioning in office buildings, use of hot tubs, and other urban water reservoirs, are all perfect breeding grounds for the Legionella bacteria. Each year the US reports between 8000-18000 cases of Legionnaires disease, with outbreaks most recently at the Illinois Veterans’ Home in Quincy, where there were 8 diagnosed cases, and one at the San Quentin State Prison, where a further 13 individuals were diagnosed. Outside the US, there were 5851 cases reported to the European Centre for Disease Prevention and Control in 2013, which is well within the rate seen in previous five years.
The good news is that it is easy to prevent outbreaks. New air conditioning systems, especially those in multi-unit buildings, have been engineered to prevent the growth of bacteria. There are best practice guidelines about where and how to position fresh air intakes relative to cooling towers to prevent contaminated air from entering the ventilation systems. In addition, many jurisdictions require that all cooling towers and evaporative condensers have annual inspections; some require inspections every 6 months. All of these practices help prevent Legionella outbreaks from occurring. Monitoring, regularly inspecting cooling platforms, and early diagnosis can all prevent the spread of Legionella pneumophila, and prevent it from spreading like it did in 1976.
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