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      What Have We Learned From the Typhoid Fever Surveillance in Africa Program?

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          Abstract

          The Typhoid Fever Surveillance in Africa Program (TSAP) was established in 2009 to fill the data void concerning invasive Salmonella disease in sub-Saharan Africa, and to specifically estimate the burden of bloodstream infections caused by the key pathogen, Salmonella enterica serovar Typhi. TSAP has achieved this ambitious target, finding high incidences of typhoid fever in both rural and urban populations in several countries in sub-Saharan Africa. The results of TSAP will undoubtedly dictate the direction of future typhoid fever research in Africa, and at last provides a key piece of the disease burden jigsaw puzzle. With the dawn of new Vi conjugate vaccines against Salmonella Typhi, the next priority for the typhoid community must be providing the required data on these vaccines so they can be licensed and provided to those in high-risk groups and locations across sub-Saharan Africa.

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          A study of typhoid fever in five Asian countries: disease burden and implications for controls.

          To inform policy-makers about introduction of preventive interventions against typhoid, including vaccination. A population-based prospective surveillance design was used. Study sites where typhoid was considered a problem by local authorities were established in China, India, Indonesia, Pakistan and Viet Nam. Standardized clinical, laboratory, and surveillance methods were used to investigate cases of fever of >or= 3 days' duration for a one-year period. A total of 441,435 persons were under surveillance, 159,856 of whom were aged 5-15 years. A total of 21,874 episodes of fever were detected. Salmonella typhi was isolated from 475 (2%) blood cultures, 57% (273/475) of which were from 5-15 year-olds. The annual typhoid incidence (per 100,000 person years) among this age group varied from 24.2 and 29.3 in sites in Viet Nam and China, respectively, to 180.3 in the site in Indonesia; and to 412.9 and 493.5 in sites in Pakistan and India, respectively. Altogether, 23% (96/413) of isolates were multidrug resistant (chloramphenicol, ampicillin and trimethoprim-sulfamethoxazole). The incidence of typhoid varied substantially between sites, being high in India and Pakistan, intermediate in Indonesia, and low in China and Viet Nam. These findings highlight the considerable, but geographically heterogeneous, burden of typhoid fever in endemic areas of Asia, and underscore the importance of evidence on disease burden in making policy decisions about interventions to control this disease.
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            Typhoid in Kenya is associated with a dominant multidrug-resistant Salmonella enterica serovar Typhi haplotype that is also widespread in Southeast Asia.

            In sub-Saharan Africa, the burden of typhoid fever, caused by Salmonella enterica serovar Typhi, remains largely unknown, in part because of a lack of blood or bone marrow culture facilities. We characterized a total of 323 S. Typhi isolates from outbreaks in Kenya over the period 1988 to 2008 for antimicrobial susceptibilities and phylogenetic relationships using single-nucleotide polymorphism (SNP) analysis. There was a dramatic increase in the number and percentage of multidrug-resistant (MDR) S. Typhi isolates over the study period. Overall, only 54 (16.7%) S. Typhi isolates were fully sensitive, while the majority, 195 (60.4%), were multiply resistant to most commonly available drugs-ampicillin, chloramphenicol, tetracycline, and cotrimoxazole; 74 (22.9%) isolates were resistant to a single antimicrobial, usually ampicillin, cotrimoxazole, or tetracycline. Resistance to these antibiotics was encoded on self-transferrable IncHI1 plasmids of the ST6 sequence type. Of the 94 representative S. Typhi isolates selected for genome-wide haplotype analysis, sensitive isolates fell into several phylogenetically different groups, whereas MDR isolates all belonged to a single haplotype, H58, associated with MDR and decreased ciprofloxacin susceptibility, which is also dominant in many parts of Southeast Asia. Derivatives of the same S. Typhi lineage, H58, are responsible for multidrug resistance in Kenya and parts of Southeast Asia, suggesting intercontinental spread of a single MDR clone. Given the emergence of this aggressive MDR haplotype, careful selection and monitoring of antibiotic usage will be required in Kenya, and potentially other regions of sub-Saharan Africa.
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              Diagnostics for invasive Salmonella infections: Current challenges and future directions.

              Invasive Salmonellosis caused by Salmonella enterica serotype Typhi or Paratyphi A, B, C, or invasive non-typhoidal Salmonella serotypes, is an immensely important disease cluster for which reliable, rapid diagnostic tests are not available. Blood culture remains the gold standard but is insensitive, slow, and resource-intensive. Existing molecular diagnostics have poor sensitivity due to the low organism burden in bodily fluids. Commercially available serologic tests for typhoidal Salmonella have had limited sensitivity and specificity. In high burden, resource-limited settings, reliance on clinical diagnosis or inaccurate tests often results in frequent, unnecessary treatment, which contributes selective pressure for the emergence of antimicrobial resistance. This practice also results in inadequate therapy for other etiologies of acute febrile illnesses, including leptospirosis and rickettsial infections. A number of novel serologic, molecular, transcriptomic and metabolomic approaches to diagnostics are under development. Target product profiles that outline specific needs may focus development and investment, and establish benchmarks for accuracy, cost, speed, and portability of new diagnostics. Of note, a critical barrier to diagnostic assay rollout will be the low cost and low perceived harm of empiric therapy on behalf of providers and patients, which leaves few perceived incentives to utilize diagnostics. Approaches that align incentives with societal goals of limiting inappropriate antimicrobial use, such as subsidizing diagnostics, may be essential for stimulating development and uptake of such assays in resource-limited settings. New diagnostics for invasive Salmonellosis should be developed and deployed alongside diagnostics for alternative etiologies of acute febrile illnesses to improve targeted use of antibiotics.
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                Author and article information

                Journal
                Clin Infect Dis
                Clin. Infect. Dis
                cid
                cid
                Clinical Infectious Diseases: An Official Publication of the Infectious Diseases Society of America
                Oxford University Press
                1058-4838
                1537-6591
                15 March 2016
                01 March 2016
                01 March 2016
                : 62
                : Suppl 1 , Typhoid Fever Surveillance in Africa Program (TSAP)
                : S1-S3
                Affiliations
                [1 ]Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit , Ho Chi Minh City, Vietnam
                [2 ]Centre for Tropical Medicine, Oxford University
                [3 ]London School of Hygiene and Tropical Medicine , United Kingdom
                [4 ]Initiative for Vaccine Research, World Health Organization , Geneva, Switzerland;
                [5 ]Department of Epidemiology, International Vaccine Institute , Seoul, Republic of Korea
                Author notes
                Correspondence: S. Baker, Hospital for Tropical Diseases, 764 Vo Van Kiet, Quan 5, Ho Chi Minh City, Vietnam ( sbaker@ 123456oucru.org ).
                Article
                civ675
                10.1093/cid/civ675
                4772830
                26933014
                bd29d152-1346-4287-8d9b-0ff74b5eac06
                © The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Funding
                Funded by: Wellcome Trust http://dx.doi.org/10.13039/100004440
                Categories
                Typhoid Fever Surveillance in Africa Program (Tsap)

                Infectious disease & Microbiology
                salmonella typhi,sub-saharan africa,epidemiology
                Infectious disease & Microbiology
                salmonella typhi, sub-saharan africa, epidemiology

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