Dynamics of Dengue Transmission in the Arid Region of Sonora, Mexico

Abstract

Most of dengue transmission occurs in tropical and subtropical zones. As a result, studies on the dynamics of dengue transmission are principally focused in these areas. Less is known about the dynamics of dengue transmission and the interplay of social and climatic determinants in arid regions located at the fringe of transmission zones. This dissertation uses surveillance data from the state of Sonora, an arid region in northern Mexico, to examine three specific aims: 1) to assess relationships among social and climatic factors utilizing locality-level dengue incidence data across the state of Sonora, 2) to determine the correlation between the spatial pattern of dengue cases during an outbreak in Hermosillo, a large urban area, and neighborhood-level socio-economic and water supply factors using a novel case-control study design, and 3) to determine how dengue cases disseminated across two arid cities, Hermosillo and Navojoa, and to determine if changing socio-demographic patterns were similar between cities. Results from the first ecological study indicated that the distribution of dengue across the state was associated most strongly with the climatic gradient and, secondarily, by population size and lack of education. Underreporting in rural areas with lower access to transportation infrastructure was also detected. We demonstrated that a spatially-based case-control study design was useful in identifying associations between dengue transmission and neighborhood-level characteristics related to population density, lack of access to healthcare and water supply restrictions. Finally, the spatio-temporal study identified common patterns between the two cities/outbreaks. Dengue transmission arose and was maintained for 2-3 months in specific foci areas characterized by low access to healthcare and then the disease moved to contiguous areas. Recommendations for surveillance and control programs based on these results include: 1) in small localities at risk of transmission a combination of active and passive surveillance should be carried out for a period of time to determine if transmission is occurring, 2) monitoring water storage practices during water restrictions and ensuring appropriate messaging about covering storage containers should be made, and 3) spatial monitoring of dengue cases and agency reaction to initial disease occurrence could reduce spread to adjacent areas.