Rapid diagnosis of Legionnaires' disease by urinary antigen detection: Comparison of ELISA and radioimmunoassay

An enzyme-linked immunosorbent assay was developed to detect urinary antigen excreted by patients with Legionnaires' disease. Of 47 patients tested, antigen was detected in 39. Of these 39 specimens, 35 gave clearly positive results by visual analysis; four others required spectrophotometric verification of positive results. Antigen was not detected in any of 178 urine specimens from patients with other pulmonary, bacteremic or urinary tract infections after a quick and simple confirmatory test. The assay required more time to perform than a previously described radioimmunoassay but was of equivalent sensitivity and specificity and did not require expensive equipment or contact with radioactive reagents. We conclude that enzyme-linked immunosorbent assay is a rapid, sensitive and specific means for rapidly diagnosing Legionnaires' disease that can be performed in clinical laboratories unwilling or unable to use radioisotopes.