Evaluation of the Hemolytic Test in the Serodiagnosis of Human Leptospirosis

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Abstract
The hemolytic test (HL) was subjected to an extensive evaluation with 46 different serotype rabbit antiserums and 455 serums from cases of human leptospirosis representing at least 24 different serotype infections. Comparative HL and homologous microscopic agglutination (MA) titrations on the serotype rabbit anti-serums demonstrated generic specificity and marked sensitivity of the HL procedure. HL tests were positive on serums from all 181 proved human cases, with maximum HL titers of 1:100 or higher in convalescent serums from all but 3 cases. Nearly all leptospirosis cases exhibited a dramatic rise in HL titer between acute and convalescent paired serums. In analyzing the distribution of HL titers by day of disease, it was found that the number of positive HL reactions increased from 5 to 86% from the 3d to the 10th day of disease. Approximately 93% of the convalescent serums showed a distribution in the HL titer range of 1:1000 through 1:100,000 with a geometric mean titer of 1:4100. Titers reached a maximum generally between the 11th and 20th day of disease, after which they declined gradually to the point where residual titers of 1:100 persisted for more than 1 year. Titers obtained by the HL and MA testing procedures appeared to be directly related, with HL reactive antibodies generally appearing a few days earlier and generally reaching a higher maximum level. HL tests on 72 human serums from a healthy population and from 107 patients with a variety of diseases other than leptospirosis revealed the absence of HL antibody titers of over 1:100. Possible explanations, for the occurrence of low order antibodies in small numbers of these nonleptospirosis groups and for the possible diagnostic significance of HL titers of over 1:100 and/or demonstrable increases in the HL titers of serial serum samples, are discussed. The present evidence indicates that the currently used microscopic agglutination tests could be advantageously supplanted by the HL test in the serologic diagnosis of human leptospirosis.

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