[Spatial distribution of leptospirosis in Rio Grande do Sul, Brazil: recovering the ecology of ecological studies].

Leptospirosis is an endemic disease in the State of Rio Grande do Sul, Brazil, and presents a broad diversity of exposure routes, reservoirs, etiological agents, and clinical features. The main objective of this work is to identify transmission areas and possible ecological components of leptospirosis transmission. This was accomplished through the aggregation of epidemiological data into spatial units that represent the State's socio-environmental diversity. The 1,274 confirmed leptospirosis cases that occurred in 2001 were georeferenced in the counties of residence. The county maps were overlaid on environmental units characterizing land use, altitude, and river basins. Incidence rates for each environmental class were calculated, along with their statistical significance, through GIS aggregation operations. The highest incidence rates were verified in coastal sedimentary areas with low altitude and predominantly agricultural land use. In these areas, most of the cases were associated with irrigated farming. The results suggest the existence of favorable ecological characteristics for leptospirosis transmission in places involving proliferation of peri-domiciliary rodents and intensive agricultural production. The article discusses the effects of data aggregation into environmental units, as well as strategies to control the endemic in the State.