Date Published: December 3, 2015
Publisher: Public Library of Science
Author(s): Adam Akullian, Eric Ng’eno, Alastair I. Matheson, Leonard Cosmas, Daniel Macharia, Barry Fields, Godfrey Bigogo, Maina Mugoh, Grace John-Stewart, Judd L. Walson, Jonathan Wakefield, Joel M. Montgomery, Ricardo J. Soares Magalhaes. http://doi.org/10.1371/journal.pntd.0004212
Abstract: BackgroundEnteric fever due to Salmonella Typhi (typhoid fever) occurs in urban areas with poor sanitation. While direct fecal-oral transmission is thought to be the predominant mode of transmission, recent evidence suggests that indirect environmental transmission may also contribute to disease spread.MethodsData from a population-based infectious disease surveillance system (28,000 individuals followed biweekly) were used to map the spatial pattern of typhoid fever in Kibera, an urban informal settlement in Nairobi Kenya, between 2010–2011. Spatial modeling was used to test whether variations in topography and accumulation of surface water explain the geographic patterns of risk.ResultsAmong children less than ten years of age, risk of typhoid fever was geographically heterogeneous across the study area (p = 0.016) and was positively associated with lower elevation, OR = 1.87, 95% CI (1.36–2.57), p <0.001. In contrast, the risk of typhoid fever did not vary geographically or with elevation among individuals less than 6b ten years of age.ConclusionsOur results provide evidence of indirect, environmental transmission of typhoid fever among children, a group with high exposure to fecal pathogens in the environment. Spatially targeting sanitation interventions may decrease enteric fever transmission.
Partial Text: Typhoid fever is a systemic, enteric disease caused by Salmonella enterica serovars Typhi and Paratyphi and has an estimated annual global incidence of 26.9 million cases, and causes 200,000 deaths per year . Morbidity and mortality due to typhoid fever occurs primarily in young children in Africa and Asia [2, 3]. Children lack natural immunity and experience high levels of exposure to fecal pathogens . If untreated, the case fatality can exceed 10%, although appropriate antibiotic treatment can reduce case fatality to 1% or less .
In this large, population-based, case-control study, risk of typhoid fever was spatially heterogeneous across a small geographic area. The observed spatial pattern in risk was especially pronounced among children under ten years of age, who experienced an almost doubling of risk for every ten meter decrease in elevation. In contrast, the spatial distribution in the risk of typhoid fever among adults and adolescents varied only slightly across the study area. Our results suggest distinct modes of transmission of typhoid fever between children and adolescents/adults in a Kenyan urban slum. Transmission in children may be more environmentally mediated than that in adults.