RESUMEN
<p><b>OBJECTIVE</b>The study was designed to find out the epidemic characteristics of leptospriosis and to develop effective intervention measures. The effects of floods on leptospriosis in some areas along Yangzi river and Huai river in Anhui province was also analysed.</p><p><b>METHODS</b>Study on serum epidemiology of leptospriosis was carried out from serous samples collected from native residents and animal hosts including isolation of pathogens at different phases (before,middle and after) and different monitoring spots,during the floods.</p><p><b>RESULTS</b>Infection rate with leptospriosis pathogen among native residents was 13.49% during the flood-period,much higher than 2.18% at post-flood (chi2 = 22.78, P < 0.01) stage, in the flood-affected areas along Yangzi river in 1998. The average rates of infection were 2.48% and 5.35% in affected and unaffected areas along Huai river respectively, in 2003.</p><p><b>CONCLUSIONS</b>There was full evidence that floods causing the epidemics of leptospriosis. However, the transmission of leptospriosis among people would depend on affecting factors as scales of floods, lasting time, coincidence between flood happening and epidemic season, immuno-protection level against leptospriosis among people and so on to a great extent. Factors as the magnitude of pathogens carried by various kinds of infectious sources were also important determinants affecting the nature, being epidemic or pandemic of leptospriosis. It was suggested that active surveillance network on the sources of infection and risk factors of leptospriosis should be developed for the control and prevention of the disease, in the flood-hit areas.</p>