Changing epidemiology of human leptospirosis in New Zealand.

The objective was to describe the current epidemiology and trends in New Zealand human leptospirosis, using descriptive epidemiology of laboratory surveillance and disease notification data, 1990-8. The annual incidence of human leptospirosis in New Zealand 1990-8 was 44 per 100,000. Incidence was highest among meat processing workers (163.5/100,000), livestock farm workers (91.7), and forestry-related workers (24.1). The most commonly detected serovars were Leptospira borgpetersenii serovar (sv.) hardjo (hardjobovis) (46.1%), L. interrogans sv. pomona (24.4%) and L. borgpetersenii sv. ballum (11.9%). The annual incidence of leptospirosis declined from 5.7/100,000 in 1990-2 to 2.9/100,000 in 1996-8. Incidence of L. borgpetersenii sv. hardjo and L. interrogans sv. pomona infection declined, while incidence of L. borgpetersenii sv. ballum infection increased. The incidence of human leptospirosis in New Zealand remains high for a temperate developed country. Increasing L. borgpetersenii sv. ballum case numbers suggest changing transmission patterns via direct or indirect exposure to contaminated surface water. Targeted and evaluated disease control programmes should be renewed.