<P> The mortality at the original American Legion convention in 1976 was high (29 deaths in 182 infected individuals) because the antibiotics used (including penicillins, cephalosporins, and aminoglycosides) had poor intracellular penetration . Mortality has plunged to less than 5% if therapy is started quickly . Delay in giving the appropriate antibiotic leads to higher mortality . </P> <P> The fatality rate of Legionnaires' disease has ranged from 5% to 30% during various outbreaks and approaches 50% for nosocomial infections, especially when treatment with antibiotics is delayed . Hospital - acquired Legionella pneumonia has a fatality rate of 28%, and the principal source of infection in such cases is the drinking - water distribution system . </P> <P> Legionnaires' disease acquired its name in July 1976, when an outbreak of pneumonia occurred among people attending a convention of the American Legion at the Bellevue - Stratford Hotel in Philadelphia . Of the 182 reported cases, mostly men, 29 died . On January 18, 1977, the causative agent was identified as a previously unknown strain of bacteria, subsequently named Legionella, and the species that caused the outbreak was named Legionella pneumophila . </P> <P> Outbreaks of Legionnaires' disease receive significant media attention . However, this disease usually occurs in single, isolated cases not associated with any recognized outbreak . When outbreaks do occur, they are usually in the summer and early autumn, though cases may occur at any time of year . Most infections occur in those who are middle - aged or older . National surveillance systems and research studies were established early, and in recent years improved ascertainment and changes in clinical methods of diagnosis have contributed to an upsurge in reported cases in many countries . Environmental studies continue to identify novel sources of infection, leading to regular revisions of guidelines and regulations . About 8,000 to 18,000 cases of Legionnaires' disease occur each year in the United States, according to the Bureau of Communicable Disease Control . </P>

Where does the name legionnaires disease come from
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