During the last three decades many surveys have been made on human intestinal parasites throughout the world. These surveys have included such population groups as armies, hospitals, inmates of jails, schools, orphan's homes, and asylums. The results of these surveys have shown that some human protozoa and helminth infections are not only tropical and subtropical in distributions, but may be quite common in the temperate zone.
Craig (1934) emphatically stressed the importance of the “amebiasis problem” in the United States. He also mentioned that about 5 to 10 per cent of the people of the United States are carriers of Endamoeba histolytica, and that every carrier, as soon as detected, should be treated and the infection eliminated. Craig (1939) tabulated the results of many surveys in the United States, and found that among 71,278 individuals examined the percentage infection was 10.5. This percentage approximates his estimate of the incidence of E. histolytica infection throughout the United States.