Risk factors for transmission of Streptococcus agalactiae infection between Danish dairy herds: a case control study.

A group of 152 Danish dairy herds infected with Streptococcus agalactiae during 1992 was compared with 177 randomly selected control herds in order to identify factors of importance for the transmission of this bacteria between herds. The diagnosis was based on a laboratory microbiological test on a bulk tank milk sample, and management information was collected by telephone interviews with the farmers. Results from logistic regression clearly indicate that purchase of cows or heifers increases the risk of a new Streptococcus agalactiae herd infection. Hygiene management risk factors inside the farm were also identified.