Revisiting the 1976 Legionnaires Disease Outbreak!

Those of us who recall the 1976 outbreak of Legionnaires disease should remember the scare of a possible flu-like pandemic. Those who recall the outbreak, are probably not aware the problem arose from the defective design of an HVAC system, in which mold growth in a rooftop cooling tower was inducted into an adjacent air intake duct servicing the building.  On July 21, 1976, the American Legion hosted a convention of 2,000+ participants, mostly elderly men, at the Bellevue-Stratford Hotel in Philadelphia Pennsylvania.  The convention was intended to be a celebratory event coinciding with the 200th anniversary of the birth of the United States. Instead, it resulted in an outbreak of what has become known as “Legionnaires Disease” , resulting in fatigue, chest pains, fever, headaches. shortness of breath, congestion, pneumonia, and death.  

The outbreak resulted in 182 hospitalizations, including 29 deaths and the discovery a bacteria named “Legionella Bacterium” or LB.  As it turned out, LB grew and thrived in the warm water circulating through the cooling tower on the roof of the hotel adjacent to an air intake. It was then distributed by moist air passing through the ductwork inside the hotel via the air conditioning system as well as on the streets surrounding the hotel through wind and mist.  This bacteria was transmitted through mist and moist air and inhaled into the lungs, resulting in the onset of symptoms within 2-14 days following exposure. However, LB was not discovered until January 18, 1977, six months after researchers from the Center for Disease Control  or CDC had taken over the hotel and two months after the hotel had been closed for good. 

As it turns out, LB thrives in water temperatures between 95 and 110 degrees Fahrenheit, often found in equipment supporting central air conditioning systems in office buildings, hotels, exhibition halls, shopping malls, factories, and hospitals. The types of HVAC equipment in which LB can be found, centers around cooling towers in HVAC systems, but can also be traced to multiple other sources, including hot tubs, humidifiers, de-humidifiers, water supplies, fountains, and misting systems, all of which maintain a reservoir of warm water.  LB  growth can be treated and prevented through the use of disinfectants, prevention of stagnation, temperature changes, and design features, separating equipment from air intakes.  

Despite the discovery of LB in 1976 there have been multiple deadly outbreaks both around the world and the United States since that time, including:

• April 1985 - At a hospital in Stafford England , 175 people fell ill, and 28 died due to a LB outbreak in a rooftop cooling tower.
• March 1999 - At an exhibition hall in Bovenkarspel, Netherlands where 318 people fell ill and 32 died due to the a LB outbreak in a rooftop cooling tower.
• September 2005 - At a nursing home in Canada, 127 people fell ill, and  21 died due to a LB outbreak in a cooling tower.
• October, 2017 - At Disneyland in Anaheim California, 22 people fell ill due to an LB outbreak in a misting system used to cool visitors.
• November 2017 - At a hospital in Lisbon Portugal, 53 people fell ill, and 5 died due to a LB outbreak in a cooling tower. 
• September 2019 - At a state fair in Asheville North Carolina, 141 people fell ill and 4 died due to an LB outbreak in a hot tub exhibit. 
• February 2024 - In Grand Rapids, Minnesota, 14 people fell ill due to an LB outbreak in a municipal water system. 

The expansion of LB outbreaks beyond the safety and warm waters of HVAC cooling towers suggests that the bacteria may be evolving and adapting to new environments.   

The medical community is on constant alert of new outbreaks of LB.  It is currently estimated that as many as 10,000 cases of LB arise in the United States every year.  As the source and incidence of LB outbreaks continue to grow, everyone must beware of the environments in which the bacteria can evolve and adapt.