Role of Environmental Factors in Shaping Spatial Distribution ofSalmonella entericaSerovar Typhi, Fiji

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.

Epidemiology and risk factors for typhoid fever in Central Division, Fiji, 2014–2017: A case-control study

“…Distal conditions within the water catchment have yet to be thoroughly evaluated in case-control studies of typhoid fever. However, geospatial studies are beginning to examine such relationships on broad spatial scales [ 7 , 33 , 34 ]. Although no distal environmental conditions were statistically associated with typhoid fever in our multivariable model, experiencing flooding of the nearest river or stream in the past two months and reporting dams upstream in the river basin were significant in univariable analysis.…”

“…However, the basis for these risks is not well understood and could be the subject of future research. At a sub-catchment scale, typhoid infection and disease in the Fijian setting has been linked with forest fragmentation, increased erosion, rainfall, and flood risk [ 7 , 34 ]. It is likely that such environmental factors result in overflow and damage to already poor sanitation facilities leading to contamination of produce and drinking water sources.…”

“…Poor hygiene practices also appear to increase odds for typhoid fever. Although not detected in this study, landscape factors contributing to flooding of poor sanitation facilities may also contribute to enhanced risk [ 7 , 34 ]. The situation in Fiji may reflect sources and modes of transmission predominant elsewhere in Oceania, where typhoid incidence is also high [ 1 ] and similar socio-demographic and environmental circumstances prevail.…”

Spatial Trends in Salmonella Infection in Pigs in Spain

“…These approaches have allowed the detection of patterns and clusters of infection and prediction of occurrence and risk of infection of Salmonella under different situations. K-function analysis (14, 15) and Moran's I (16,17) have been used to detect spatial clustering in Salmonella infection in farm animals, and a Gaussian kernel function has been used to predict the occurrence of Salmonella-infected dairy cattle and pig herds (18,19). Using human cases, Simpson et al (21) used the Besag-York-Mollié (BYM) hierarchical model (20) to map the cases of S. Wangata and S. Typhimurium in New South Wales, Australia (21).…”

Environmental Foundations of Typhoid Fever in the Fijian Residential Setting

“…While behaviours associated with faecal contamination of food and water have dominated perspectives on typhoid transmission [2], determinants related to the residential setting, namely the conditions of the lived environment including infrastructure, and microbiological and physicochemical characteristics, warrant attention for their potential to influence risk of transmission. The classic case-control study remains the most widely used epidemiological approach for assessing risk of transmissible diseases such as typhoid fever, and for testing causal hypotheses in the proximal environment [3], although recent geospatial studies have also shed light on risk factors at broader spatial scales [4,5,6,7].…”