Evaluation of the indirect hemagglutination assay for diagnosis of acute leptospirosis in Hawaii

Timely diagnosis of leptospirosis is important to ensure a favorable clinic al outcome. The definitive serologic assay, the microscopic agglutination t est (MAT), requires paired sera and is not useful for guiding early clinica l management. The only screening test approved for use in the United States , the indirect hemagglutination assay (IHA), has not undergone extensive fi eld evaluation. To assess the performance of the leptospirosis IHA in Hawai i, serum from patients evaluated for leptospirosis between 1992 and 1997 we re tested with the IHA at the Hawaii State Laboratories Division and with t he MAT at the Centers for Disease Control and Prevention. Leptospirosis was considered confirmed by a fourfold rise in MAT titer and/or a positive cul ture. A total of 92 (41%) of 226 specimens from 114 persons with confirmed leptospirosis were found positive by IHA. Only 18 (15%) of 119 specimens ob tained within 14 days of onset were IHA positive, compared to 74 (69%) of 1 07 specimens collected more than 14 days after onset (P <0.001). Repeat tes ting ultimately resulted in 78 (68%) of the confirmed cases having at least one specimen found positive by IHA. Thirteen different presumptive infecti ng serogroups were identified among 251 specimens with an MAT titer of grea ter than or equal to 200 and obtained from persons with confirmed or probab le leptospirosis. Fifty (68%) of 73 specimens with Icterohaemorrhagiae as t he presumptive infecting serogroup were found positive by IHA, compared to 44 (47%) of 93 specimens,vith Australis as the presumptive infecting serogr oup (P, 0.01), The IHA test was positive for 3 (1%) of 236 specimens from 1 54 persons without leptospirosis. The sensitivity of the leptospirosis IHA in Hawaii was substantially below figures reported previously, particularly early in the course of illness, limiting its usefulness for diagnosing acu te infection. Since the presumptive infecting serogroup affected IHA result s and the prevalence of serovars varies with geography, the performance of the IHA should be assessed locally. More sensitive leptospirosis screening tests are needed in Hawaii.