Surveillance of enteric fever and other invasive salmonellosis

Objective:

Aims to carry out a pilot feasibility assessment to explore integration of enteric fever and invasive non typhoidal salmonellosis (iNTS) into the IB-VPD Surveillance Network.

Funding source:

World health Organization

Rationale and Background information:

Enteric fever is caused by Salmonella enterica serovar Typhi (S. Typhi) or S. paratyphi A, B and C. Invasive non-typhoidal salmonellosis is caused by invasive non-typhoidal serovars of S. enterica (including S. Typhimurium and S. Enteritidis). Invasive salmonellae are responsible for a significant burden of morbidity and mortality worldwide. S. Typhi is estimated to cause up to 26.9 million typhoid cases and up to 269,000 deaths annually (1-3). S. Paratyphi is responsible for 5.4 million cases of paratyphoid fever per year and is reported to be increasingly prevalent, with S. Paratyphi A causing nearly 50% of infections in some parts of Asia (4,5). Invasive non-typhoidal salmonellosis (iNTS) is most commonly caused by S. enterica serovars Enteritidis and Typhimurium. An estimated 3.4 million cases of iNTS disease occur annually, with the highest incidence in Africa usually in infants, young children and young adults with underlying comorbidities, including severe anaemia, malaria, malnutrition and HIV-infection in whom the case fatality rate is high (6-8). The disease remains an important public health problem in developing countries estimating 16 million cases with 600,000 related deaths worldwide (9). S. typhi was the most common bacteria identified in culture and accounted for an estimated 211 hospitalization per 100,000 children <5 years of age in Bangladesh (10) Surveillance for enteric fever and iNTS will be conducted under the WHO-supported programme of surveillance for invasive bacterial vaccine-preventable diseases (IB-VPD), a hospital-based sentinel surveillance network that seeks to gather high quality standardized data on severe invasive infections caused by selected pathogens. Surveillance for invasive infections caused by S. Typhi, S. Paratyphi or iNTS in children aged 0 months to 15 years will gather data to provide policy makers information to make decisions on vaccine use. In particular, baseline epidemiological data on typhoid (for which licensed vaccines are available and introduction of the next generation conjugate vaccines is anticipated) will be critical in the short term for decision-making in countries where typhoid fever is endemic. There are currently no licensed vaccines against paratyphoid fever and iNTS disease, however several candidates are in development and surveillance for paratyphoid fever and iNTS will help establish robust baseline epidemiological data for future vaccine introduction decisions.

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