Risks of contracting leptospirosis on the dairy farm.

The sera of 460 people associated with farming were examined for evidence of leptospiral agglutinins. Of these, 308 were dairy farm workers, 62 percent of whom were from the Waikato. Forty-four percent of dairy farm workers, 8 percent of sheep and beef farmers and 25 percent of pig farmers ware seropositive. Of the 137 seropositive dairy farm workers, 65 percent had titres to serovar hardjo and 53 percent to pomona. There were no significant differences between the serological prevalences of workers in different geographical regions. Analysis of factors significantly associated with seropositive workers included; being male, a previous history of medically confirmed leptospirosis in the worker, a clinical history of leptospirosis in the cattle, the size of the milking herd, the type of milking shed, and vaccination of the herd against leptospirosis. These findings indicate that the incidence of leptospirosis in dairy farm workers can only be effectively controlled by reducing the prevalence of infection in dairy cattle.