Prevalence of leptospirosis in man. Pilot survey.

A survey on the prevalence of leptospirosis was performed on the population living in an area of central Italy. The size of the sample was calculated in order to provide significant results in the case of a prevalence of infection in not less than 1% of the population. Results demonstrated an unexpectedly wide circulation of leptospirosis in the surveyed area, showing a prevalence rate of infection of 11.34% for people living in rural areas and 3.08% for people living in the main town. The highest prevalence of infection (17.44%) was found in people between 30 and 44 years of age, living in rural areas. Such a wide circulation of undiagnosed past leptospiral infections was attributed both to the prevalence of mild clinical cases of leptospirosis in humans and the lack of microbiological tests performed to differentiate current leptospirosis from other infectious illnesses. An unexpected persistence in sera of co-agglutinins towards non-pathogenic serovars of L. biflexa was also noticed in healthy people. Criteria were established for the extension of the survey on the prevalence of leptospirosis to cover larger areas by limiting sampling to the more exposed age groups and to areas representative of a larger land belt.