Differential Epidemiology of Salmonella Typhi and Paratyphi A in Kathmandu, Nepal: A Matched Case Control Investigation in a Highly Endemic Enteric Fever Setting

Abstract

BackgroundEnteric fever, a systemic infection caused by the bacteria Salmonella Typhi and Salmonella Paratyphi A, is endemic in Kathmandu, Nepal. Previous work identified proximity to poor quality water sources as a community-level risk for infection. Here, we sought to examine individual-level risk factors related to hygiene and sanitation to improve our understanding of the epidemiology of enteric fever in this setting.Methodology and principal findingsA matched case-control analysis was performed through enrollment of 103 blood culture positive enteric fever patients and 294 afebrile community-based age and gender-matched controls. A detailed questionnaire was administered to both cases and controls and the association between enteric fever infection and potential exposures were examined through conditional logistic regression. Several behavioral practices were identified as protective against infection with enteric fever, including water storage and hygienic habits. Additionally, we found that exposures related to poor water and socioeconomic status are more influential in the risk of infection with S. Typhi, whereas food consumption habits and migration play more of a role in risk of S. Paratyphi A infection.Conclusions and significanceOur work suggests that S. Typhi and S. Paratyphi A follow different routes of infection in this highly endemic setting and that sustained exposure to both serovars probably leads to the development of passive immunity. In the absence of a polyvalent vaccine against S. Typhi and S. Paratyphi A, we advocate better systems for water treatment and storage, improvements in the quality of street food, and vaccination with currently available S. Typhi vaccines.

Increase in Salmonella enterica serovar Paratyphi A infections in Phnom Penh, Cambodia, January 2011 to August 2013

“…Consumption of food from street vendors has been found an independent risk factor for acquisition of paratyphoid fever in other Asian countries e.g. Nepal and Indonesia [13,14] . Of note, we observed also a two-fold increase of infections due to S. Typhi.…”

Salmonella chronic carriage: epidemiology, diagnosis, and gallbladder persistence

“…Therefore, ongoing transmission of disease in endemic regions is likely to be driven largely by these recently-infected patients [40]. This scenario is supported by epidemiological studies that have shown disease transmission to close contacts within the household primarily from convalescent carriers rather than chronically infected individuals [13, 41]. Further, improved genetic analysis employing haplotyping of S. Typhi isolates and whole genome sequencing in highly endemic regions such as Vietnam and Nepal also found that acute typhoid is generally associated with a random distribution of organisms, rather than the same genotypes in close proximity [42].…”

Prevalence ofSalmonellaExcretion in Stool: A Community Survey in 2 Sites, Guinea-Bissau and Senegal

“…In many developing countries, open defecation can lead to contamination of water systems, resulting in an increased risk of Salmonella transmission through the ingestion of bacteria in water used for drinking, washing, or irrigating produce [10][11][12]. Factors related to water source and storage, sanitation practices, and street food consumption have also been associated with increased risk of infection [13].…”