Social and Environmental Factors of Dengue Fever in the Sonoran Desert of Mexico, 2006-2011

Background: Dengue fever is currently endemic in the Mexican Sonoran Desert but transmission risk is not the same across the region. The aim of this study was to determine social and environmental factors associated with varying levels of dengue incidence at the locality level in Sonora, MX between 2006 and 2011. Understanding factors associated with risk under current conditions can inform the potential for expansion of dengue into other areas.

Methodology: Incidence of dengue was calculated for each locality (N=1,158), census and remotely sensed information, Zero-inflated negative binomial modelling (ZINB) was then used in order to simultaneously assess: 1) the association of dengue incidence with social and environmental factors; and 2) the probability that factors such as population size and distance to the main highway may lead to exessive zeros that are related to barriers of disease surveillance and thus the accurate reporting of dengue cases.

Results: Incidence varied over the study period and was higher in southern and western parts of the state. According to the best model, dengue incidence increases 31.4% (IRR=1.314, 95% CI: 1.204, 1.435) per 1 inch of increment in cumulative rainfall and 56.8% (IRR=1.568, 95% CI: 1.255, 1.959) per 1 C° increment in average maximum temperature. Incidence is positively associated with percent of population with no basic education (IRR=1.038, 95% CI: 1.012, 1.064) and log-transformed population size (IRR=1.255, 95% CI: 1.049, 1.503). There is a positive association between the probability of excessive zeros and the distance to the highway (OR=1.033, 95% CI: 1.016, 1.051) and a negative association with log-transformed population size (OR=0.368, 95% CI: 0.212, 0.639).

Discussion: Dengue incidence was associated with higher levels of rainfall, vapor pressure and temperature, and social factors related to urbanization and lack of education. However, potential problems of underreporting could be present in rural localities with higher distance to the land transportation infrastructure.  Further exploration of the accuracy of the surveillance system in place is warranted, particularly in localities that share factors associated with dengue risk but have no reported transmission.