ABSTRACT
Members of the genus Legionella are Gram-negative, aerobic bacilli that belong to the gamma-subgroup of proteobacteria. Legionella are facultative, intracellular bacteria that are ubiquitously found in freshwater ponds and streams where they colonize phagocytic protozoa. The relevance of these organisms to human health was first recognized following the eponymous 1976 outbreak at a meeting of the American Legion in Philadelphia. During the weeks following the convention, 221 attendees fell ill with unexplained, pneumonia-like symptoms; 34 of these patients later died (Garrett 1994). Legionnaires’ disease was ultimately linked to infection by a bacterium that was named Legionella pneumophila. An examination of the air conditioning system at the convention site revealed high levels of L. pneumophila-laden protozoa, indicating that exposure to these bacteria via inhalation of contaminated aerosols could result in severe respiratory disease.
