What is the pathophysiology of Legionella infection?

Updated: Nov 13, 2018
  • Author: Mobeen H Rathore, MD, CPE, FAAP, FIDSA; Chief Editor: Russell W Steele, MD  more...
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Answer

Legionella organisms are aerobic, motile, and nutritionally fastidious pleomorphic gram-negative rods. The growth of the organisms depends on the presence of L-cysteine and iron in special media. The organism has been isolated in natural aquatic habitats (freshwater streams and lakes, water reservoirs) and artificial sources (cooling towers, potable water distribution systems). Freshwater amoebae appear to be the natural reservoir for the organisms. [3] Optimal growth temperature is 28-40°C; organisms are dormant below 20°C and are killed at temperatures above 60°C.

Although more than 70 Legionella serogroups have been identified among 50 species, L pneumophila causes most legionellosis. L pneumophila serogroup 1 alone is responsible for 70-90% of cases in adults. In a pediatric series, L pneumophila serogroup 1 accounted for only 48% of cases, serogroup 6 accounted for 33%, and the remaining cases involved other serotypes and species. Legionella micdadei and L dumoffii are the second and third most common species to cause Legionnaires disease in children, respectively. [4]


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