Global burden of Shigella infections: implications for vaccine developmentand implementation of control strategies

Few studies provide data on the global morbidity and mortality caused by in fection with Shigella spp.; such estimates are needed, however, to plan str ategies of prevention and treatment. Here we report the results of a review of the literature published between 1966 and 1997 on Shigella infection. T he data obtained permit calculation of the number of cases of Shigella infe ction and the associated mortality occurring worldwide each year, by age, a nd (as a proxy for disease severity) by clinical category, i.e. mild cases remaining at home, moderate cases requiring outpatient care, and severe cas es demanding hospitalization. A sensitivity analysis was performed to estim ate the high and low range of morbid and fatal cases in each category. Fina lly, the frequency distribution of Shigella infection, by serogroup and ser otype and by region of the world, was determined. The annual number of Shigella episodes throughout the world was estimated t o be 164.7 million, of which 163.2 million were in developing countries (wi th 1.1 million deaths) and 1.5 million in industrialized countries. A total of 69% of ail episodes and 61% of all deaths attributable to shigellosis i nvolved children under 5 years of age. The median percentages of isolates o f S. flexneri, S. sonnei, S. boydii, and S. dysenteriae were, respectively, 60%, 15%, 6%, and 6% (30% of 5 dysenteriae cases were type 1) in developin g countries; and 16%, 77%, 2%, and 1% in industrialized countries. In devel oping countries, the predominant serotype of S. flexneri is 2a, followed by 1b, 3a, 4a, and 6. In industrialized countries, most isolates are 5 flexne ri 2a or other unspecified type 2 strains. Shigellosis, which continues to have an important global impact, cannot be adequately controlled with the existing prevention and treatment measures. Innovative strategies, including development of vaccines against the most c ommon serotypes, could provide substantial benefits.