Specimen Information

Type

Gold, SST

Volume

1.0 ml

Transport Info

Centrifuge and immediately transfer serum to separate plastic tube
Refrigerated

Fasting Required?

False

Clinical Significance

The 1976 outbreak of an acute febrile respiratory illness in Philadelphia at a Pennsylvania American Legion convention was extensively investigated by the Centers for Disease Control (CDC). This resulted in the isolation and identification of the etiologic agent, Legionella disease bacterium (LDB), a gram-negative bacillus. The disease, legionellosis, exhibits a variety of responses from asymptomatic infection or mild influenza-like illnesses to severe multisystemic disease, including, most commonly, pneumonia. The Legionella IFA test detects antibodies against L. pneumophila in human serum. Samples will be screened for Types 1-6; all positives will be titered by IFA for Type 1 only. The CDC and many state health laboratories recommend testing only for antibody to L. pneumophila Type 1. A fourfold rise in titer greater than 1:128 from the acute to the convalescent phase provides evidence of a recent infection with Legionella. A standing or single titer ł 1:256 suggests past exposure or infection, but is inconclusive for diagnosis. Single titers of less than 1:256 are not considered evidence of infection. Diagnosis of acute infection can only be made with a fourfold or greater rise in titer between acute and convalescent specimens. IgM antibody to Legionella pneumophila serotypes 1-6 is measured using an IgM-specific conjugate. It is recommended that the IgM test always be performed in conjunction with the IgG antibody test. The IgM response to Legionella tends to develop concurrently with the IgG response and may remain elevated as long as the IgG response remains elevated. Cross-reactions have been described with several species of bacteria and mycoplasma.