Leptospirosis occurs worldwide and is an occupational disease for those who handle animals, who are in contact with water or soil contaminated with animal urine. or work in waste water management. Weil's disease used to be a disease caught by farm workers and sewer men, but there has been a gradual increase among recreational water-users, particularly fishermen and canoeists. Sex differences are not apparent where equal risk is present. However, men are more frequently affected than women because their occupations may bring them more often into contact with infected animals and a contaminated environment. The age group most commonly affected is that between 20 and 30 years. Individuals and young children may be affected if they swim or play in contaminated ponds or streams.
In 1997 in the UK, there were 39 reported cases of Weil's disease; in 1992 there were 28 cases (resulting in seven deaths), an increase of 10 on the previous year.