Sero-prevalence of leptospirosis in workers at a New Zealand slaughterhouse

To undertake a pilot study to measure the sero-prevalence to Leptospira serovars Hardjo and Pomona in an occupationally exposed group. To evaluate worker age, sex and previous clinical episodes of leptospirosis as risk factors for sero-positivity.

A cross-sectional sero-prevalence study was conducted in February and March 2008 at a predominantly sheep slaughterhouse in Hawke's Bay, New Zealand. A single blood sample was collected from 242 meatworkers, comprising 145 men and 97 women. Sera were tested by the Microscopic Agglutination Test (MAT) with a titre cut point of 1:24, using serovars Pomona and Hardjo as antigens. Age, sex, and details of previous clinical episodes of leptospirosis were recorded.

Overall sero-prevalence was 9.5%. Ten (4.1%) workers were positive to serovar Hardjo (titres 1:24-1:192), 13 (5.4%) were positive to serovar Pomona (titres 1:24-1:768), and one worker was positive for both serovars. Sero-prevalence was 13.1% and 4.1% in men and women, respectively. The median age for sero-positive workers was 54 years while that for sero-negative workers was 48 years. Twenty-three workers (9.5%) reported a leptospirosis disease episode 1-35 years previously, and 14 of those were sero-positive in the current study.

The sero-prevalence observed suggests significant exposure to leptospirosis from sheep in meatworkers in the slaughterhouse studied. This sero-prevalence was similar to that reported in a survey in 1982. Further study is needed to determine the link between sero-prevalence and incidence, whether the prevalence of leptospirosis is similar in other slaughterhouses, and to develop a better understanding of risk factors important for the reduction of exposure of this occupationally acquired disease.