A Study of Typhoid Fever in Five Asian Countries: Disease Burden and Implications for controls/Etude De la Fievre Typhoide Dans Cinq Pays Asiatiques: Charge De Morbidite et Implications Pour la Lutte Contre Cette maladie/Estudio Sobre la Fiebre Tifoidea En Cinco Paises Asiaticos: Carga De Morbilidad E Implicaciones Para El Control De la Enfermedad

Introduction Typhoid fever is a systemic infection caused by Salmonella enterica serotype Typhi (S. typhi). The disease remains an important public health problem in developing countries. In 2000, it was estimated that over 2.16 million episodes of typhoid occurred worldwide, resulting in 216 000 deaths, and that more than 90% of this morbidity and mortality occurred in Asia. (1) Although improved water quality and sanitation constitute ultimate solutions to this problem, vaccination in high-risk areas is a potential control strategy recommended by WHO for the short-to-intermediate term. (2) Two safe and efficacious typhoid vaccines, the injectable Vi polysaccharide and the oral Ty21a, have been licensed; and new, improved candidate vaccines are currently being tested. (3-5) However, typhoid vaccination has not been implemented as a routine public health measure in most typhoid-endemic countries despite the low price of the vaccine (Vi polysaccharide costs ca. US$ 0.50 per dose) and the high cost of treating the disease. (6) Policy-makers in several developing countries have indicated that updated data on the incidence of typhoid in their countries are essential before they introduce the vaccines into programmes. (7) Indeed, population-based estimates of blood culture-confirmed typhoid are sparse. In Asia, disease burden estimates have usually relied on routinely reported, clinically diagnosed cases of typhoid fever compiled by governments or hospitals, usually with uncertain denominators. Clinical diagnosis of typhoid is not specific because the presenting signs and symptoms are diverse and similar to those of other common febrile illnesses, such as malaria and dengue fever. A specific diagnosis of typhoid requires access to a competent laboratory that can process blood cultures; such laboratories are uncommon in resource-poor regions. Population-based studies of the incidence of culture-confirmed typhoid have therefore usually come from the control arms of typhoid vaccine trials. (3,5,8-14) [FIGURE 1 OMITTED] We conducted prospective population-based surveillance in five Asian countries using standardized surveillance techniques, as well as standardized clinical and microbiological methods, to provide an updated assessment of the burden of typhoid in Asia. The studies were also performed in preparation for a series of effectiveness trials of Vi polysaccharide vaccine. (4,15) In this paper, we present the disease burden estimates from a 12-month pre-vaccination surveillance period in each site in these five countries. Methods Study sites Sites in five Asian countries, which are considered to be endemic for typhoid; China, India, Indonesia, Pakistan, and Viet Nam, participated in the programme. As a result of discussions with local collaborators, we selected study populations that satisfied the following criteria: a high perceived burden of typhoid fever, absence of control programmes against the disease, willingness of the community to participate, and feasibility of a vaccination trial (Fig. 1). With the exception of the site in Pakistan, no reliable estimates of the incidence of blood-culture proven typhoid were available. (16) Prior to the onset of surveillance, a census was conducted at each site to enumerate the entire population. Each household and each individual resident in the study areas were assigned unique study numbers and recorded in the project data management system. The study site in China, Hechi, in Guangxi Zhuang Autonomous Region, included urban (Jin-Cheng Jiang) and rural (Dong Jiang) townships: 112 889 residents were registered in the baseline census in 2001. In India, wards 29 and 30 of Kolkata, West Bengal, which consist of legally recognized urban slums, were selected as the study site (population, 56 946 in the baseline census in 2003). Two impoverished municipal districts in North Jakarta, Tanjung Priok and Koja, constituted the study site in Indonesia: 160 261 persons were registered in the baseline census in 2002. …