Explore the recorded discovery and history of Legionella pneumophila, with source links and stated limits.
L. pneumophila lives in water and grows inside free-living amoebae and protozoa, persisting in biofilms. CDC states that people can get Legionnaires’ disease, a type of serious pneumonia, when they breathe in mist containing the bacteria from building water systems, hot tubs and similar sources, and that in general it is not spread person to person. The same bacteria can cause Pontiac fever, a milder illness. Sixteen serogroups are recognized, and PHAC describes serogroup 1 as the most virulent and prevalent.
A severe respiratory illness struck people connected to an American Legion convention at the Bellevue-Stratford hotel in Philadelphia. CDC’s museum account states that 221 people across Pennsylvania were sick and 34 had died, while CDC’s Emerging Infectious Diseases etymology gives 182 ill Legionnaires and 29 deaths; the two figures count different groups and both are recorded here rather than merged.
CDC records that microbiologist Joseph McDade isolated and identified the organism in early 1977, culturing it from lung tissue without antibiotics after standard procedures had failed. Identification came months after the investigation began.
LPSN records Brenner et al. 1979 as the naming authority, published in Annals of Internal Medicine, with type strain Philadelphia 1 (ATCC 33152 / NCTC 11192). The genus honours the Legionnaires of the 1976 convention and the species name comes from Greek for lung-loving.
These references do not establish the first person ever infected. Discovery, naming and isolation milestones do not date biological origin or a patient zero.
Source check: 2026-09-19. Educational content; independent scientific review remains pending.