Cholera Transmission in Bangladesh: Social Networks and Neighborhoods

Transmission of infectious pathogens across networks is well-documented, yet remains primarily focused on diseases spread by sexual contact. Such analytical tools, however, may also facilitate understanding of how other types of health outcomes are related to physical and social contacts. This research examines the relationship between cholera incidence and the social network that links households in rural Bangladesh. Using twenty-one years of longitudinal demographic and health data, clustering of similar disease rates in the network was measured and compared to spatial autocorrelation of cholera at the neighborhood level. Results indicate that rates are significantly concentrated amongst households within the same local environment, and that social clustering is only evident during certain years examined. These outcomes suggest that intervention efforts should place priority on identifying local-level environmental factors, but also consider the potential of networks as they assist transmission, as well as their role in interactions within a defined neighborhood

The Role of Vaccine Coverage within Social Networks in Cholera Vaccine Efficacy

Traditional vaccine trial methods have an underlying assumption that the effect of a vaccine is the same throughout the trial area. There are, however, many spatial and behavioral factors that alter the rates of contact among infectious and susceptible individuals and result in different efficacies across a population. We reanalyzed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from cholera vaccines when vaccination rates are high in an individual's social network.We analyzed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse trend for the relation between the level of vaccine coverage in an individual's social network and the incidence of cholera in individual vaccine recipients or placebo recipients after controlling for potential confounding variables.Using bari-level social network ties, we found incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (5.28 cases per 1000 in the lowest quintile vs 3.27 cases per 1000 in the highest quintile; p = 0.037 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's social network were independently related to a reduced risk of cholera.Findings indicate that progressively higher levels of vaccine coverage in bari-level social networks can lead to increasing levels of indirect protection of non-vaccinated individuals and could also lead to progressively higher levels of total protection of vaccine recipients