Comparison of serology and isolates for the identification of infecting leptospiral serogroups in Hawaii, 1979-1998

Laboratory confirmation of leptospirosis is usually accomplished serologically, without isolates, using the microscopic agglutination test (MAT). However, optimal performance of the MAT is dependent on the knowledge of enzootic serogroups and serovars so that an appropriate MAT antigen testing battery can be established. Infecting leptospiral serogroups can be identified serologically without isolates, using the MAT, or by serogrouping of isolates, but little information is available regarding the correlation between these methods. The identification of infecting serogroups for 53 culture-confirmed leptospirosis cases, diagnosed in Hawaii between 1979 and 1998, using serology and culture isolates were compared. The overall agreement between the two methods was good (kappa = 0.71, 95% CI: 0.56, 0.86). However, the agreement varied between serogroups from 0 to 100%. In establishing the prevalence of serogroups, results obtained via MAT serology (in the absence of serogrouped isolates) should be considered presumptive rather than definitive.