Distribution and Incidence

Infection with E. histolytica occurs around the world, although both commensal and pathological amebiasis is more common in poor, tropical countries. Prevalence rates vary greatly, as does the proportion of infections that result in clinical disease.

Amebiasis, especially clinical disease, is rare today in developed countries and is confined largely to specific groups such as residents of institutions, male homosexuals, travelers, and immigrants. In the United States from 3,000 to 4,000 cases were reported annually in the 1960s through the late 1970s. However, a spurt to roughly twice that level occurred in 1979-84. The disease was concentrated in Texas and California and was probably due to increased immigration from Mexico and Southeast Asia.

On the other hand, cases may be significantly underreported. One recent estimate suggests that the real annual total probably exceeds 100,000, and, in a 1970 study, 4 percent of military recruits had positive serologic tests. As recently as the early 1950s, infection rates of 10 to 20 percent were found in some rural southern counties. In Britain the car rier rate is between 2 and 5 percent; 31 amebiasis deaths were recorded from 1962 to 1971.

Asymptomatic and clinical amebiasis is much more common in Third World countries. Surveys have shown prevalence rates of from 2 to 60 percent, reflecting real differences as well as technical difficulties. It is clearly a major public health problem in much of South and Southeast Asia, China, Africa, and parts of Latin America. Mexico appears to have an unusually high prevalence. In the early 1980s it was estimated that 5 to 6 million clinical cases and 10,000 to 30,000 deaths took place annually in a population of some 70 million. Men in their 20s and 30s were most likely to die. In 1981, it was estimated that there were about 480 million infected people in the world: 290 million in Asia, 80 million in Africa, 90 million in the Americas, and remarkably, 20 million in Europe. Serious disease struck 10 million in the Americas, 15 to 30 million Asians, 10 million Africans, and few if any Europeans. The global death toll was between 40,000 and 110,000.

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