Background: Brazil has the second highest number of new leprosy cases reported annually with the state of Minas Gerais (MG) having pockets of highly endemic leprosy. Transmission remains only partially understood, and in addition to a respiratory route, transmission may also be related to environmental conditions. Potentially viable Mycobacterium leprae has been found in water, soil, and armadillos.
Objective: To investigate the role of the environment on transmission of leprosy, specifically, (1) elevation, (2) normalized difference vegetation index (NDVI), (3) temperature, and (4) precipitation.
Methods: We conducted a cross-sectional study using Brazilian Notifiable Disease Surveillance System (SINAN) data in 853 municipalities in the state of Minas Gerais, Brazil from 2009 to 2013. Multivariable Poisson regression models were used to estimate the rate ratio (or incidence density ratio (IDR)) to compare incidence across municipalities. We then used spatial statistics (global autocorrelation, local indicator of spatial autocorrelation [LISA], Getis Ord Gi(d)* to analyze clustering of leprosy cases and incidence.
Results: Overall incidence decreased from 8.76 per 100,000 in 2009 to 5.04/100,000 in 2013 with the average municipality leprosy incidence at 7.11 per 100,000 annually. The local autocorrelation analysis identified 51 high-high clusters of leprosy incidence in the northeast and west of Minas Gerais. After controlling for clustering among all municipalities in Minas Gerais, temperature (IDR=1.76, 95% CI: 1.64, 1.89, p= <0.0001) and precipitation (IDR=1.06, 95% CI: 1.01, 1.12, p= 0.0201) were positively correlated with leprosy incidence. Elevation (IDR=0.53, 95% CI: 0.51, 0.55, p= <0.0001) was negatively correlated with leprosy incidence. NDVI (IDR= 0.98, 95% CI: 0.95, 1.00, p= 0.18) was negatively correlated with leprosy incidence, yet not significant.
Conclusions: The associations between leprosy and environmental predictors, especially higher temperatures, indicate that the role of the environment and geographical conditions need to be considered in the context of disease transmission and viability of M. leprae in the environment, especially in the era of global warming and climate change.
Table of Contents
Table of Contents
A. Introduction 1
B. Methods 6
C. Results 12
D. Discussion 17
About this Master's Thesis
|Committee Chair / Thesis Advisor|
|File download under embargo until 20 May 2020||2019-04-24||File download under embargo until 20 May 2020|