American cutaneous leishmaniasis in Southeast Brazil: space-time clustering

Background American cutaneous leishmaniasis (ACL) is endemic in many rural areas of Brazil where different transmission patterns of the disease have b een described. This ecological study was carried out in a municipality loca ted in Southeast Brazil and aimed to investigate the space-temporal pattern s of the disease and environmental risk factors from 1966 to 1996. Methods Incident ACL cases were defined by clinical diagnosis, confirmed by a positive skin test and/or parasitological examination. Age-adjusted morb idity rate of ACL was calculated by year for this municipality and their di fferent census enumeration districts. The homogeneity chi(2) test, Moran an d empirical Bayes index and Knox procedure were employed for testing the si gnificance of clusters in time, space and in time-space, respectively. A Po isson regression model was used to identify environmental factors related t o rate variability. Results A total of 1712 new ACL cases were reported with a yearly incidence rate of 48/100 000 inhabitants. Higher incidence rates were detected in 19 68, 1974, and 1988 (100, 160, and 190 cases/100 000, respectively) with evi dence of spatial clustering from 1986 to 1993. Significant space-time clust ering with epidemic peaks followed by low incidence in subsequent periods w as observed. The incidence rates of ACL were independently associated with rural areas: areas lacking sanitary installations and with higher proportio n of exposed garbage (P < 0.01). Conclusions This study suggests that ACL rates vary across space and time. Rural areas and some environmental factors could explain part of this varia tion. Environmental modifications in the vicinity of households over time a nd accumulation of susceptible individuals are discussed as possible factor s responsible for variability.