A survey was conducted to estimate the frequency of Leptospira sp. infection in cattle in the State of Paraíba, Brazil. A random sample of 6 municipalities was chosen from each of 3 ecoregions of the state: the Agreste/Litoral, the Cariri/Curimatau and the Sertão. These 18 municipalities were broken down into quadrants and one property was selected at random from each quadrant. Random samples were collected from at least eight animals at each property, in four-age categories, summing at least

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... animals per property. All municipalities that were included in the study (100%) and 87.75% of the properties had at least one positive sample for one of the 15 different Leptospira sp. serovars (16 strains) studied. From 2,343 samples, 759 showed positive reaction to, at least, one of the 16 strains tested. Four hundred and seventy animals were positive to multiple strains. The serovar Hardjo, of the Sejroe serogroup, was the most frequent and accounted for 16.05% (95% CI 12.69% to 19.41%) of the positive results (376 positive reactions). There were differences in the frequency of positive results according to the two strains of serovar Hardjo used: strain Norma (15.62% 95% CI 12.38% to 18.86%), isolated in Brazil, and reference strain Hardjoprajitino (2.43% 95% CI 1.12% to 3.75%). The remaining serovars tested had frequencies lower than 2.8%. Results obtained in the present study confirmed that Leptospira interrogans serovar Hardjo is widely spread in the State of Paraíba, Brazil.