American cutaneous leishmaniasis in Southeast Brazil: space-time clustering

American cutaneous leishmaniasis (ACL) is endemic in many rural areas of Brazil where different transmission patterns of the disease have been described. This ecological study was carried out in a municipality located in Southeast Brazil and aimed to investigate the space-temporal patterns of the disease and environmental risk factors from 1966 to 1996.

Incident ACL cases were defined by clinical diagnosis, confirmed by a positive skin test and/or parasitological examination. Age-adjusted morbidity rate of ACL was calculated by year for this municipality and their different census enumeration districts. The homogeneity chi2 test, Moran and empirical Bayes index and Knox procedure were employed for testing the significance of clusters in time, space and in time-space, respectively. A Poisson regression model was used to identify environmental factors related to rate variability.

A total of 1712 new ACL cases were reported with a yearly incidence rate of 48/100000 inhabitants. Higher incidence rates were detected in 1968, 1974, and 1988 (100, 160, and 190 cases/100000, respectively) with evidence of spatial clustering from 1986 to 1993. Significant space-time clustering with epidemic peaks followed by low incidence in subsequent periods was observed. The incidence rates of ACL were independently associated with rural areas; areas lacking sanitary installations and with higher proportion of exposed garbage (P < 0.01).

This study suggests that ACL rates vary across space and time. Rural areas and some environmental factors could explain part of this variation. Environmental modifications in the vicinity of households over time and accumulation of susceptible individuals are discussed as possible factors responsible for variability.