Legionella pneumophila  was perceived in 1976 after an episode of pneumonia at an American Legion show in Philadelphia.The Legionellaceae are picky gram-negative microscopic organisms that live in amphibian situations everywhere throughout the globe. In their indigenous habitat, the Legionellaceae are intracellular parasites of free-living protozoa. These creatures may likewise occupy man-made water appropriation frameworks. The family Legionellaceae comprises of a solitary sort, Legionella. All the more explicitly, this sort incorporates the species Legionella pneumophila, which are non-embodied, vigorous bacilli. Notwithstanding L. pneumophila, there are 41 different species in the class and together these species partition into 64 serogroups. Inside the species L. pneumophila, human contamination is caused essentially (however not solely) by a set number of serogroups . L. pneumophila is the most regular reason for human legionellosis, otherwise called Legionnaire's infection in the Legionellaceae family. It is likewise a generally basic reason for network procured and nosocomial pneumonia in grown-ups. Furthermore, L. pneumophila serogroup 1 alone is liable for 70-90% of cases. The Legionellaceae were not archived until 1976, when an inconvenient flare-up of pneumonia happened in Philadelphia at an American Legion Convention. The offender, L. pneumophila, was separated first by vaccination of after death lung tissue into guinea pigs and afterward by subculture into a rich counterfeit medium At that point by circuitous immunofluorescent immunizer examine, it was discovered that over 90% of those that became sick had in any event multiple times the centralization of counter acting agent in the blood (fourfold ascent in titer) against this creature. A similar technique was utilized to screen recently spared sera from before flare-ups of unexplained respiratory illness and they found that various them were related with seroconversion to L. pneumophila.