After cellular fatty acid and DNA typing studies, the isolate was identified as Legionella feeleii . To date there are 39 species of Legionella and many more serotypes, but only 19 species have been isolated from humans. 6 and L. micdadei , although other species can be predominant in disease in a specific geographic area. Extrapulmonary disease has been reported, but respiratory disease, called legionellosis, is the most common presentation. The spectrum of legionellosis ranges from asymptomatic infection to fulminate pneumonia.
Infection appears to be from exposure to aerosolized water containing the organism.
Nosocomial outbreaks have been reported, and are often reduced with increased chlorination or super heating of the water supply. Because the organism is ubiquitous, control is difficult. The laboratory diagnosis of Legionella remains one of the most challenging problems for the clinical microbiology laboratory. Although several methods are available, most suffer from an untimely diagnosis or lack of sensitivity. The gold standard for diagnosis is a four-fold rise in antibody titer to one of the species antigens.