Leptospirosis of pig farmers: the results of a serological survey.

Serum samples were examined from 70 people working or resident on 41 pig farms within a 50 km radius of Palmerston North. Of the 65 people with occupational pig contact, 20 (31 percent) had microscopic agglutination titres of 1:24 or greater to one or more serovars of Leptospira interrogans, the majority of which were to pomona, the pid adapted serovar. There were significant positive associations between those people with a titre and those with a history of previous diagnosis of leptospirosis by a medical practitioner and the number of breeding sows and fattening pigs on the property. Pig farmers are at similar risk to contracting leptospirosis as dairy farmers, but the major serovars involved are different, and the total population at risk is less. Further evidence is provided that titres to leptospiral agglutinins can persist in humans for longer than ten years.