Distribution and Incidence

Shigellosis occurs worldwide, but is especially common in countries with poor water and sewage systems. The virulent S. dysenteriae is mostly confined to the tropics and East Asia; a much less pathogenic form, S. sonnei, is the most abundant species in the United States. All age groups are vulnerable, but severe disease is most common in children and among the elderly. There appears to be no racial or ethnic immunity, although populations can acquire considerable resistance to locally prevalent strains. Travelers may become ill when they encounter unfamiliar strains. Accurate incidence rates are impossible to obtain, but shigellosis is a serious health problem in most underdeveloped countries and a major cause of infant and child mortality. The disease is commonly endemic in poor countries, but great epidemics can also take place. During World War II, acute dysentery, apparently introduced by Japanese and/or Allied troops, attacked many indigenous groups in western New Guinea, causing thousands of deaths despite the efforts of Australian authorities. In 1969 an epidemic of S. dysenteriae caused 110,000 cases and 8,000 deaths in Guatemala.

Shigellosis is also a constant threat in developed countries, especially when sanitary standards are weakened. For example, two important S. sonnei outbreaks occurred in the United States in 1987. One took place among Orthodox Jews in New York, New Jersey, Ohio, and Maryland, with the majority of cases occurring among small children in religious schools. Patterns of spread were consistent with person-to-person transmission among religious communities in the four states. The first outbreak was in New York City, where 132 cases were reported and at least 13,000 were suspected. Smaller epidemics in upstate New York and other states appeared to be linked with Passover visits to relatives in the city. The second epidemic began with the annual meeting of a counter-culture group, the Rainbow Family, in a national forest in North Carolina in early July. Poor hygiene and inadequate latrines

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