RESUMEN
This investigation is the first nationwide survey on the circulation of leptospira infections in human beings in Italy. In nine out of twenty Italian regions, representative samples of the population were investigated for the presence of leptospira infections. Unexpectedly, leptospira infections were found to be widespread, the number of cases being much higher than the diagnosed clinical cases. There were found to be high, medium, and low risk areas. On the whole, the risk for the rural population was no higher than the risk for urban dwellers; leisure activities, contact with animals and residence on the plain versus residence in the hills were important risk factors. There was an unidentified risk factor in urbanites which was absent in the rural population. A changing pattern in infecting serovars was observed, with infections from serogroups Sejroe, Javanica and Australis prevailing over infections from the Icterohaemorrhagiae and Bataviae serogroups, which were the main agents of human leptospirosis during the 1950s. The mechanisms of these changes, the need for epidemiological surveys and improved diagnostic methods of screening are discussed.