On this day in medical history: Legionnaires’ disease has namesake outbreak

By John Murphy, MDLinx
Published August 2, 2018

Key Takeaways

An outbreak of Legionnaires’ disease in New York City recently sickened 18 people and killed 1. This rash of cases in Upper Manhattan, currently under investigation, arrives nearly on the anniversary of the most historic outbreak of the disease—the epidemic that occurred at the American Legion convention in Philadelphia, PA, starting July 21, 1976.

In July 1976, Philadelphia was decked out in red, white, and blue as the City of Brotherly Love celebrated the United States Bicentennial—the 200th birthday of the signing of the Declaration of Independence. Queen Elizabeth II and Prince Philip visited and presented the city with a Bicentennial Bell made in the same foundry as the original Liberty Bell.

From July 21 to 24, Philadelphia also hosted the annual convention of the American Legion. The convention was headquartered at the stately Bellevue-Stratford Hotel, with an estimated 4,400 attendees.

In the days following the convention, several of the Legionnaires came down with mysterious flu-like symptoms, including tiredness, muscle aches, headache, cough, chest pain, and fever. On August 2, the Pennsylvania Department of Health recognized that some type of outbreak had occurred among the convention’s attendees and alerted local health officials and medical societies of a potential statewide epidemic.

A total of 182 people were identified with the illness; 147 were hospitalized and 29 died. Many of those hospitalized had evidence of pneumonia. Various antibiotics seemed to help patients improve, but no single antibiotic was particularly effective.

Epidemiologists from the Centers for Disease Control (CDC) homed in on the infection, noting that many attendees who fell ill had spent time in the hotel lobby and on the sidewalk in front of the hotel. Of interest, no hotel employees came down with symptoms, except for one: an air-conditioning repairman. “Many hotel employees appeared to be immune, suggesting that the agent may have been present in the vicinity, perhaps intermittently, for 2 or more years,” CDC epidemiologists wrote in a 1977 article in The New England Journal of Medicine.


After months of painstaking investigation, the source of infection was found: the air-conditioning cooling towers on the hotel roof. We now know that outbreaks of Legionnaires’ disease are often associated with large, complex water systems—like those used by hospitals, hotels, resorts, and cruise ships—that aren’t adequately maintained. Legionella pneumophila (as the bacterium was later named) is transmitted via inhalation of aerosolized water. Researchers believe water droplets from the hotel’s cooling towers trickled down to the sidewalk and also got into the air-conditioning vents that cooled the lobby.

More than 40 years later, the number of cases of Legionnaires’ disease continues to rise. Over 6,100 cases were reported in 2016 in the United States, according to the CDC.

“This [rise] is in part due to weather-related events as well as high-profile outbreaks,” said Legionella expert Janet E. Stout, PhD, president and director, Special Pathogens Laboratory, Pittsburgh, PA, in an interview with MDLinx. Dr. Stout discovered that hospital water systems (not cooling towers) were the source for Legionella in hospital-acquired Legionnaire's disease.

“The New York City Bronx outbreak [in 2015] and the outbreak in Flint, Michigan [2014/2015], certainly helped increase physician awareness and the likelihood that patients will be tested for Legionella,” she said. "More testing equals more cases diagnosed and reported.”

But the increase in reported cases—more than 300% in the last 10 years—is just the tip of the iceberg, she added. “Many more cases are missed than are diagnosed and reported.”

To avoid misdiagnosing a case of Legionnaires’ disease, Dr. Stout offers this advice: “The clinical presentation of Legionnaires’ disease is often more severe than other forms of bacterial pneumonia, with the exception of the elderly whose presenting symptom may be altered mental status,” she said. “The severity of illness (with hyponatremia) and admission to the ICU are often clues to order diagnostic tests for Legionella (culture and the urine antigen test).”

Once you’ve made the diagnosis, what’s the preferred treatment? “After performing testing of many antimicrobial agents for efficacy against Legionella, I concluded that if I ever had Legionnaires’ disease, I’d want to be treated with a quinolone,” said Dr. Stout.

For more information, visit the CDC’s Legionella website for clinicians.

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