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      Environmental Transmission of Typhoid Fever in an Urban Slum

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          Abstract

          Background

          Enteric 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.

          Methods

          Data 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.

          Results

          Among 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.

          Conclusions

          Our 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.

          Author Summary

          Typhoid fever, a serious bloodstream infection caused by the bacterium Salmonella Typhi, is commonly associated with direct, person-to-person transmission as a result of improper hygiene and unsafe food/water handling practices. Recent evidence, however, suggests that individuals may be indirectly exposed to typhoid through contact with fecal contamination in their immediate environment. In this study we investigated the role of environmental sources in the transmission of typhoid fever across an urban slum in Kenya by mapping the occurrence of cases in both children and adults. We tested the hypothesis that cases (relative to non-cases) cluster in low elevation areas as a result of the downstream flow and accumulation of fecal waste. We found that cases of typhoid fever among children tended to be concentrated in the downstream area. In adolescents and adults, on the other hand, there was little evidence of a geographic pattern in the risk of typhoid fever. These results provide evidence that environmental transmission of typhoid fever contributes to the risk of disease in children but not adults and adolescents, an observation most likely attributed to the fact that children are more likely to be exposed to fecal contamination through outside play. Interventions to improve local sanitation may therefore provide particular benefit to children who are at most risk of exposure to and acquisition of typhoid fever from environmental sources.

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          Most cited references44

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          Fast stable restricted maximum likelihood and marginal likelihood estimation of semiparametric generalized linear models

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            Typhoid fever and paratyphoid fever: Systematic review to estimate global morbidity and mortality for 2010

            Background Typhoid and paratyphoid fever remain important causes of morbidity worldwide. Accurate disease burden estimates are needed to guide policy decisions and prevention and control strategies. Methods We conducted a systematic literature review of the PubMed and Scopus databases using pre-defined criteria to identify population-based studies with typhoid fever incidence data published between 1980 and 2009. We also abstracted data from annual reports of notifiable diseases in countries with advanced surveillance systems. Typhoid and paratyphoid fever input data were grouped into regions and regional incidence and mortality rates were estimated. Incidence data were extrapolated across regions for those lacking data. Age-specific incidence rates were derived for regions where age-specific data were available. Crude and adjusted estimates of the global typhoid fever burden were calculated. Results Twenty-five studies were identified, all of which contained incidence data on typhoid fever and 12 on paratyphoid fever. Five advanced surveillance systems contributed data on typhoid fever; 2 on paratyphoid fever. Regional typhoid fever incidence rates ranged from <0.1/100 000 cases/y in Central and Eastern Europe and Central Asia to 724.6/100 000 cases/y in Sub-Saharan Africa. Regional paratyphoid incidence rates ranged from 0.8/100 000 cases/y in North Africa/Middle East to 77.4/100 000 cases/y in Sub-Saharan Africa and South Asia. The estimated total number of typhoid fever episodes in 2010 was 13.5 million (interquartile range 9.1–17.8 million). The adjusted estimate accounting for the low sensitivity of blood cultures for isolation of the bacteria was 26.9 million (interquartile range 18.3–35.7 million) episodes. These findings are comparable to the most recent analysis of global typhoid fever morbidity, which reported crude and adjusted estimates of 10.8 million and 21.7 million typhoid fever episodes globally in 2000. Conclusion Typhoid fever remains a significant health burden, especially in low- and middle-income countries. Despite the availability of more recent data on both enteric fevers, additional research is needed in many regions, particularly Africa, Latin America and other developing countries.
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              The Burden of Common Infectious Disease Syndromes at the Clinic and Household Level from Population-Based Surveillance in Rural and Urban Kenya

              Background Characterizing infectious disease burden in Africa is important for prioritizing and targeting limited resources for curative and preventive services and monitoring the impact of interventions. Methods From June 1, 2006 to May 31, 2008, we estimated rates of acute lower respiratory tract illness (ALRI), diarrhea and acute febrile illness (AFI) among >50,000 persons participating in population-based surveillance in impoverished, rural western Kenya (Asembo) and an informal settlement in Nairobi, Kenya (Kibera). Field workers visited households every two weeks, collecting recent illness information and performing limited exams. Participants could access free high-quality care in a designated referral clinic in each site. Incidence and longitudinal prevalence were calculated and compared using Poisson regression. Results Incidence rates resulting in clinic visitation were the following: ALRI — 0.36 and 0.51 episodes per year for children <5 years and 0.067 and 0.026 for persons ≥5 years in Asembo and Kibera, respectively; diarrhea — 0.40 and 0.71 episodes per year for children <5 years and 0.09 and 0.062 for persons ≥5 years in Asembo and Kibera, respectively; AFI — 0.17 and 0.09 episodes per year for children <5 years and 0.03 and 0.015 for persons ≥5 years in Asembo and Kibera, respectively. Annually, based on household visits, children <5 years in Asembo and Kibera had 60 and 27 cough days, 10 and 8 diarrhea days, and 37 and 11 fever days, respectively. Household-based rates were higher than clinic rates for diarrhea and AFI, this difference being several-fold greater in the rural than urban site. Conclusions Individuals in poor Kenyan communities still suffer from a high burden of infectious diseases, which likely hampers their development. Urban slum and rural disease incidence and clinic utilization are sufficiently disparate in Africa to warrant data from both settings for estimating burden and focusing interventions.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS Negl Trop Dis
                PLoS Negl Trop Dis
                plos
                plosntds
                PLoS Neglected Tropical Diseases
                Public Library of Science (San Francisco, CA USA )
                1935-2727
                1935-2735
                3 December 2015
                December 2015
                : 9
                : 12
                : e0004212
                Affiliations
                [1 ]University of Washington, School of Public Health and Community Medicine, Department of Epidemiology, Seattle, Washington, United States of America
                [2 ]Kenya Medical Research Institute, Center for Global Health Research (KEMRI-CGHR), Kenya
                [3 ]Division of Global Health Protection, Center for Global Health, Centers for Disease Control and Prevention-Kenya, Nairobi, Kenya
                [4 ]Departments of Global Health, Medicine, Pediatrics and Epidemiology, University of Washington, Seattle, Washington, United States of America
                [5 ]University of Washington, Department of Statistics and Biostatistics, Seattle, Washington, United States of America
                University of Queensland School of Veterinary Science, AUSTRALIA
                Author notes

                The authors have declared that no competing interests exist.

                Analyzed the data: AA EN AIM GJS JW JMM. Wrote the paper: AA EN GJS JLW JM. Contributed to acquisition of data: AA EN MM JM LC DM BF GB. Contributed to critical revision of the manuscript for important intellectual content: AA AIM EN JLW GJS LC DM.

                Article
                PNTD-D-15-01212
                10.1371/journal.pntd.0004212
                4669139
                26633656
                9e356735-e245-4af4-a8e2-2be37de988c4

                This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication

                History
                : 10 July 2015
                : 14 October 2015
                Page count
                Figures: 4, Tables: 2, Pages: 14
                Funding
                This material is based upon work supported by the US Centers for Disease Control and Prevention (CDC) “Active population-based study of major infectious disease syndromes in Kenya” (Grant No. 4566), the NIH U19 “Molecular Basis for Nontyphoidal Salmonella emergence” (Grant No. AI090882), the National Science Foundation Graduate Research Fellowship Program (Grant No. DGE-0718124), and the NIH K24 Grant: “Pediatric HIV-1 in Africa: Pathogenesis and Management” (Grant. No. HD054314-06). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
                Categories
                Research Article
                Custom metadata
                Public deposition of our data would breach compliance with the protocol approved by the CDC/KEMRI IRB as the data include geo-referenced locations. Data are available upon request from the US Centers for Disease Control and Prevention (CDC) by contacting the following individual; Dr. Dr. Jennifer Verani, Epidemiologist, Division of Global Health Protection, CDC-Kenya at qzr7@ 123456cdc.gov .

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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