When Legionnaires’ disease struck Philadelphia in 1976, the country was already on edge about infectious disease. In January of that year, an outbreak of swine flu at Fort Dix army base in New Jersey killed one person and hospitalized 13 others. Fearing a repeat of the 1918 flu epidemic, President Ford launched—and then canceled—a controversial mass vaccination program, while public health officials braced for a swine flu epidemic that did not materialize. Meanwhile, cases of bubonic plague in California and other western states were making national headlines.
When CDC laboratory scientists began receiving sputum collected from those sickened in Philadelphia, they tested it for evidence of some 50 microbial pathogens, including influenza, Q fever, rickettsia, and Lassa fever. Within days, “we knew it was not swine flu,” David Fraser, who directed the CDC field investigations, told an audience in 2016. “Within the week, we were pretty certain it wasn’t anything we knew about.”
With no immediate explanation for the Legionnaires’ illness, there was ample room for “baked, half baked, and unbaked theories,” says George Dehner, a historian at Wichita State University who is writing a book about Legionella. People speculated that Soviet spies had intentionally released a chemical or biological weapon. Others suggested that Fort Detrick, which had housed the U.S. biological weapons program between 1943 and 1969, had released a harmful agent, perhaps accidentally.
Some armchair epidemiologists argued that Legionnaires’ disease was ornithosis, an infection caused by inhaling bacteria in bird poop, or that people had fallen ill by consuming toxic New Jersey Shore fish. Others blamed the CIA, freon in the hotel’s air conditioning, or exposure to nickel carbonyl, a hazardous industrial catalyst.
“We had theories from one end of the alimentary canal to the other,” Lewis Polk, Philadelphia’s acting health commissioner, told the New York Times. “We got letters saying the disease was caused by dentures, onions, toilet paper! Calls from Indiana or Oregon at 4 a.m. recommending vitamin C, acupuncture, dilute vinegar, or Mentholatum for cures!”
Weeks, then months, passed. Despite hundreds of hours of epidemiological work, the CDC team came up empty-handed. Their null result triggered wide disdain: even the journal Science minced no words: “Legion Fever: Postmortem on an Investigation That Failed,” its headline read.