Environmental Foundations of Typhoid Fever in the Fijian Residential Setting

Proximal characteristics and conditions in the residential setting deserve greater attention for their potential to influence typhoid transmission. Using a case-control design in Central Division,
Republic of Fiji, we examined bacterial (coliform and Escherichia coli) contamination and chemical composition of water and soil as potential vehicles of exposure to Salmonella Typhi, combining
observational analysis of residential living conditions, geospatial analysis of household locations, and factor analysis to explore multivariate associations with the risk of developing typhoid fever. Factors positively associated with typhoid infection related to drainage [phosphate (OR 4.235, p = 0.042) and E. coli concentrations (OR 2.248, p = 0.029) in toilet drainage soil, housing [external condition (OR 3.712, p < 0.001)], drinking water contamination (OR 2.732, p = 0.003) and sanitary condition
(OR 1.973, p = 0.031). These five factors explained 42.5% of the cumulative variance and were significant in predicting typhoid infection. Our results support the hypothesis that a combination
of spatial and biophysical attributes of the residential setting influence the probability of typhoid transmission; in this study, factors associated with poor drainage, flooding, and sanitary condition increase local exposure to contaminated water and soil, and thereby infection. These findings extend testing of causal assumptions beyond the immediate domestic domain, enhance the scope of traditional case control epidemiology and allow greater specificity of interventions at the scale of the
residential setting.