Legionnaires’ Disease Epidemic of 1976
The Legionnaires’ Disease Epidemic of 1976 was a significant public health crisis that emerged in Philadelphia shortly after the city's bicentennial celebrations. The outbreak occurred during the American Legion Convention held at the Bellevue-Stratford Hotel from July 21 to 24, where attendees began to report severe pneumonia-like symptoms. As the illness spread, health officials and the media became increasingly alarmed, with reports indicating that dozens were hospitalized and there were numerous fatalities. By early August, it was confirmed that the mysterious pneumonia, later termed Legionnaires' disease, had resulted in at least 29 deaths and affected 221 individuals, many of whom were not directly affiliated with the convention.
The causative agent, Legionella pneumophila, was not identified until January 1977, complicating the initial investigation as it mimicked other illnesses and could not be cultured through standard laboratory methods. This bacterium is now acknowledged as a major cause of community-acquired pneumonia, particularly affecting older adults and those with compromised immune systems. The outbreak highlighted the importance of monitoring water systems, as the bacterium thrives in various human-made environments, such as cooling towers and plumbing systems. Today, Legionnaires' disease remains a concern, with thousands of cases reported annually, underscoring the need for ongoing vigilance and rapid treatment to reduce mortality rates.
On this Page
Subject Terms
Legionnaires’ Disease Epidemic of 1976
Epidemic
Date: July 21-August 4, 1976
Place: Philadelphia, Pennsylvania
Result: 29 dead, 221 infected
Yearlong U.S. bicentennial celebrations reached a peak on July 4, 1976, in the city of Philadelphia. Philadelphians proudly displayed American flags on the porches of their row houses, welcoming the thousands of visitors who came to witness the United States celebration of the two hundredth anniversary of the signing of the Declaration of Independence. President Gerald Ford gave a speech at Independence Hall in Philadelphia to record the occasion for posterity. Later that afternoon, the historic Liberty Bell monument, which had been silent for many decades, was struck. Bells in towns across the country simultaneously echoed the toll of the Liberty Bell. By nightfall the excitement escalated. The light from red, white, and blue fireworks lit up skies from coast to coast.
Less than three weeks later, after so many jubilant festivities, Pennsylvanians were stunned and helpless when the city witnessed a major event in medical history and found it was again the focus of media attention. The stifling July heat and drizzling rain that fell during the legionnaires’ parade added to the sticky humidity but did not offer much relief to spectators and legionnaire families lining the center city streets in Philadelphia. The veterans with the American Legion held parades to kick off their annual gatherings. The Bellvue-Stratford Hotel, a national and historic Philadelphia landmark built in the early 1900’s, hosted the fifty-eighth Pennsylvania State American Legion Convention, where an outbreak of a pneumonia-like illness mysteriously occurred among a group of attendees. More than 4,000 delegates attended the four-day convention at the hotel, which lasted from July 21 to 24, 1976. One week after the convention, American Legion officials in Pennsylvania began receiving calls from members statewide: They reported several legionnaires had died and dozens of others were hospitalized with severe pneumonia. Leaders from the American Legion quickly alerted city and state health department personnel and media to the rapidly increasing number of legionnaires stricken by the mysterious illness.
The epidemic pneumonia that emerged following the American Legion convention was subsequently described as “one of the most publicized epidemics” in which the elite Centers for Disease Control (CDC) medical investigators had participated. State and national newspapers covering the story reported the link of the illness to legionnaire members, calling the mysterious pneumonia “Legionnaires’ disease,” and they constantly pressed researchers for information on the official death tolls and progress reports on the investigation of the outbreak. Ten days after the convention concluded, publishing a brief account in the Morbidity and Mortality Weekly Report of August 6, 1976, researchers from the CDC in Atlanta stated 22 people had died from pneumonia caused by Philadelphia Respiratory Disease. State and city physicians and epidemiologists investigating the cause of the illness that was later officially named Legionnaires’ disease were not initially able to identify the agent responsible because it mimicked other illnesses and could not be cultured using standard laboratory techniques.
Four months passed before investigators were able to find the answers and to unlock the mystery that accompanied the sometimes-fatal infection. Then, on January 14, 1976, Joseph McDade, a CDC research microbiologist, isolated a bacterium that caused the epidemic. The bacteria responsible for the disease was named Legionella pneumophila (lung-loving). It was difficult to isolate and culture, and the patterns seen in chest X rays of the victims resembled patterns that had previously been associated with viral infections. Eventually, in this outbreak legionellosis caused 29 deaths (various sources list 29-34 deaths) and sickened 221 people, some of whom were not directly associated with the convention.
Classification and Definition. In 1999, scientists characterized Legionella pneumophila as a naturally occurring aquatic microorganism. Legionella species are now recognized as a leading cause of community-acquired pneumonia. The CDC has estimated that 17,000 to 23,000 cases of Legionnaires’ disease occur annually in America, with less than 1,000 of these cases being confirmed and reported. The resulting mortality rate, which ranges up to 25 percent in untreated immunity-compromised patients, can be lowered if the disease is diagnosed rapidly and appropriate antimicrobial therapy instituted early. Legionella pneumophila is estimated to be responsible for 80 to 85 percent of reported cases of Legionella infections, with the majority of cases being caused specifically by Legionellapneumophilia.
Risk Factors, Symptoms, and Treatment. Those at risk for Legionnaires’ disease include people fifty years of age and older, smokers, and those with pulmonary disease. People with weakened immune systems, such as organ transplant patients, kidney dialysis patients, and those suffering from cancer and AIDS, are also at risk, as are those who are exposed to water vapor containing L. pneumophila. Males are 2.5 times more likely to contract the disease than females.
People with legionellosis usually first display a mild cough and low fever and, if untreated, can quickly advance through progressive pneumonia and coma. The incubation period for L. pneumophila is two to ten days. Other early symptoms of this disease include malaise, muscle aches, and a slight headache. In later stages, victims have displayed high fevers (105 degrees Fahrenheit); dry, unproductive coughs; and shortness of breath. Gastrointestinal symptoms observed include vomiting, diarrhea, nausea, and abdominal pain. Since identification of L. pneumophila, clinicians have reported it is effectively treated with either erythromycin or a combination of erythromycin and rifampin.
Reservoirs and Amplifiers. Scientists sampling lakes, ponds, streams, marine and fresh waters, and soils have isolated the L. pneumophila bacterium in nature. Amplifiers are defined by scientists as any natural or human-made system that provides suitable conditions for the growth of the bacterium. Controversy still surrounds the exact location of the bacterial agent responsible for the Philadelphia outbreak; however, most articles list the hotel air conditioner water cooling tower as the source.
Scientific publications after 1978 reported the isolation of L. pneumophila from human-made plumbing systems, including showers, faucets, hot-water tanks, cooling towers, evaporative condensers, humidifiers, whirlpools, spas, decorative fountains, dental water units, grocery produce misters, and respiratory-therapy equipment. The plumbing systems of hotels, dental offices, hospitals, grocery stores, gymnasiums, and homes have also been documented as sources for the bacterium. Environmental factors associated with survival of this bacterium are water temperatures between 68 and 122 degrees Fahrenheit (20 and 50 degrees Celsius), stagnant water, pH ranges of 2.0-8.5, microbiotically nutrient sediments, and host microorganisms (algae, protozoa, flavobacteria, and Pseudomonas bacteria).
Transmission. In 1980, CDC investigators published six key events required for the transmission of Legionella. The first three events—survival in nature, amplification, and aerosolization—are influenced by environmental parameters (reservoir temperature and pH, microorganism populations, climate, humidity, and biocides). In contrast, the last three events—susceptible exposure, intracellular multiplication in human phagocytes, and diagnosis of Legionnaires’ disease—are clinical parameters (patient risk factors, virulence, symptoms, laboratory testing, and diagnosis).
Bibliography
Fraser, David W., et al. “Legionnaires’ Disease: Description of an Epidemic of Pneumonia.” New England Journal of Medicine 297 (1977): 1189-1197.
Katz, Sheila Moriber, ed. Legionellosis. Boca Raton, Fla.: CRC Press, 1985.
McCoy, William F. Preventing Legionellosis. Seattle: IWA, 2005.
Shader, Laurel. Legionnaire’s Disease. Philadelphia: Chelsea House, 2006.
Stout, Jane E., and Victor L. Yu. “Legionellosis.” The New England Journal of Medicine 337 (1997): 682-687.
Thomas, Gordon, and Max Morgan-Witts. Anatomy of an Epidemic. New York: Doubleday, 1982.
Yu, Victor L. “Resolving the Controversy on Environmental Cultures for Legionella: A Modest Proposal.” Infection Control and Hospital Epidemiology 19, no. 12 (1998): 893-897.