|
Background
|
L. pneumophila was identified as the causative agent for Legionellosis (Legionella pneumonia, or Legionnaire's Disease) in 1977. Presently, there are more than 25 species and 33 serogroups in the family Legionellaceae, with at least 18 species associated with pneumonia, accounting for roughly 1-5% of all cases of pneumonia. L. pneumophila displays a multitude of morphologies including the bacillus, coccobacillus, and elongated fusiform. Although often difficult to perform, the Gram stain will be Gram-negative. The antibody response to L. pneumophila may be both specific and nonspecific, since the patient may have antibodies to similar antigens from other Gram-negative bacteria. Optimum times for specimen collection appear to be within the first week of illness, or as soon as possible after the onset (acute specimen), and at least 3 weeks after the onset (convalescent specimen). By the IFA method, a single result of 1:256 is considered presumptive evidence of legionella infection. Diagnostic titers have been reported to be absent in as many as 25% of patients, but the use of multiple Legionella species as the antigen source and a polyvalent conjugate directed against IgG, IgM, and IgA maximize the accuracy of serological procedures.
|
