ELSEV IER zyxwvutsrq BACTERIOLOGY zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Stability of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Legionella Urinary Antigens Over Time E.W. Rigby, J.F. Plouffe, B.A. Hackman, D.S. Hill, R.F. Benson, and R.F. Breiman zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF Twenty-two urine samples positive for Legionella pneumo- phila serogroup 1 antigen by EQUATE radioimmunoassay (RlA) (Binax, Portland, ME, USA) were stored at various temperatures and the RIA repeated at 1, 7, 30, 90, and 120 days to evaluate stability of the urina y antigens. The mean INTRODUCTION Untreated Legionnaires’ disease has a mortality rate as high as 25%. The etiologic agent of 50 to 60% of all cases of Legionnaires’ disease is Legion&r pneumo- phiZu serogroup 1 (Reingold et al. 1984). Various methods can be employed for the diagnosis of Le- gionnaires’ disease. The Legionella urinary antigen as- say (Binax, Portland, ME) is a useful diagnostic tool, because it is rapid, specific, and sensitive (Kohler et al. 1981; Aguero-Rosenfeld et al. 1988; Ruf et al. 1990; Plouffe et al. 1995; Dominguez et al. 1996). While comparing the new enzyme-linked immunosorbent assay (ELISA) to previously positive samples by ra- dioimmunoassay (RIA) that had been frozen for up to 3 years, it was discovered that the ratios had de- creased from 18.0 to 4.6 (p = .002X Because many hospitals do not routinely test for Legionella antigen, but send samples to outside labs, we were concerned From the Ohio State University Medical Center, Columbus, Ohio (EWR, JFP, BAH, DSH), Centers for Disease Control and Prevention (RF Benson, RF Breiman), Atlanta, Georgia, USA. Address reprint requests to Joseph F. Plouffe, M.D., N-1135 Doan Hall, 410 W. 10th Avenue, Columbus, Ohio 43210, USA. Presented at the 96th General Meeting, American Society for Microbiology, New Orleans, May 1996. Received 27 September 1996; revised and accepted 16 De- cember 1996. ratios of patient/negative control remained stable. Although there was a 10% decrease in the mean ratios after 1 month, changes were not significant. However, individual samples with ratios close to 3 may fall to 43. 0 1997 Elsevier Sci- ence Inc. about the stability of the urinary antigen over time and at various storage temperatures. MATERIALS AND METHODS Twenty-two patients with pneumonia with positive assays for Legionella urinary antigen using the Equate RIA Legionella Urinary Antigen Kit (Binax) were studied. Assays were performed according to manu- facturer’s directions. A urine sample from each pa- tient was pipetted into a tube precoated with poly- clonal rabbit antibody specific for L. pneumophilu serogroup 1 antigen. After incubation for 1 hour, the tube was aspirated and washed to remove any re- maining unbound sample. I125 labeled polyclonal rabbit antibody was then added to the tubes, which were again incubated and rinsed. Bound radioactiv- ity was measured as counts per minute (cpm) on a gamma counter. A sample was considered positive when the cpm were greater than or equal to three times the activity of the negative controls. The 22 positive urine samples were divided into aliquots in 13 x 100 mm plastic tubes. One aliquot was stored at room temperature (24°C) and another at 4°C. The remaining aliquots were stored at -20°C. The assay was repeated on samples stored at each temperature after 1, 7, and 30 days. In addition, the DIAGN MICROBIOL INFECT DIS 1997;28:1-3 0 1997 Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010 0732~8893/97/$17.00 PII SO732-8893(97)00019-9