Role of Environmental Factors in Shaping Spatial Distribution of Salmonella enterica Serovar Typhi, Fiji.

Ruklanthi De Alwis,Mere Taufa,Conall Watson,Stephen Baker,Tan Trinh Van,Birgit Nikolay,John H Lowry,Dung Tran Thi Ngoc,Jerimaia Coriakula,W John Edmunds,Eric J Nilles,Kitione Rawalai,Colleen L Lau,Mike Kama,Nga Tran Vu Thieu,Jorge Cano

doi:10.3201/eid2402.170704

Abstract

Fiji recently experienced a sharp increase in reported typhoid fever cases. To investigate geographic distribution and environmental risk factors associated with Salmonella enterica serovar Typhi infection, we conducted a cross-sectional cluster survey with associated serologic testing for Vi capsular antigen–specific antibodies (a marker for exposure to Salmonella Typhi in Fiji in 2013. Hotspots with high seroprevalence of Vi-specific antibodies were identified in northeastern mainland Fiji. Risk for Vi seropositivity increased with increased annual rainfall (odds ratio [OR] 1.26/quintile increase, 95% CI 1.12–1.42), and decreased with increased distance from major rivers and creeks (OR 0.89/km increase, 95% CI 0.80–0.99) and distance to modeled flood-risk areas (OR 0.80/quintile increase, 95% CI 0.69–0.92) after being adjusted for age, typhoid fever vaccination, and home toilet type. Risk for exposure to Salmonella Typhi and its spatial distribution in Fiji are driven by environmental factors. Our findings can directly affect typhoid fever control efforts in Fiji.

Highlights

Fiji recently experienced a sharp increase in reported typhoid fever cases
After we adjusted for potential confounders, we found that annual rainfall showed a positive association
In the past 2 decades, Fiji has observed a steady increase in confirmed typhoid fever cases [16,17,18]

Summary

Introduction

Fiji recently experienced a sharp increase in reported typhoid fever cases. To investigate geographic distribution and environmental risk factors associated with Salmonella enterica serovar Typhi infection, we conducted a cross-sectional cluster survey with associated serologic testing for Vi capsular antigen–specific antibodies Risk for exposure to Salmonella Typhi and its spatial distribution in Fiji are driven by environmental factors. The Vi polysaccharide is an outer capsular antigen that enables greater human infectivity than those Salmonella Typhi strains not expressing the antigen [9]. Because of the highly antigenic nature of Vi, infection with Vi-positive Salmonella Typhi strains elicits Vi-specific antibodies in humans [10]. The Fiji Ministry of Health increased surveillance and implemented additional prevention strategies, such as vaccination against typhoid fever in the worst affected regions [17,18]. Every year during November–April, Fiji experiences powerful cyclones, which have led to destruction of homes and contamination of water sources by extensive rainfall and flooding, followed by an increase in diarrheal diseases [20,21]. Flooding has been shown to lead to outbreaks of other foodborne and waterborne diseases [22,23,24], a direct link between flooding and increased typhoid fever incidence has not been confirmed in Fiji

Methods

Results

Conclusion