Epidemic of amoebiasis and giardiasis in a biased population.

Of 126 homosexual men in a selected population in New York City, 31.7% were infected with Entamoeba histolytica, 18.3% with Giardia lamblia, and 39.7% with one or both on a single stool examination. Of 5885 clinic and hospital patients examined in the same laboratory by the same methods, 1.3% were infected with E. histolytica, 2.1% with G. lamblia, and 3.3% with one or both. Evidence indicates that an epidemic of intestinal protozoan infection exists in the homosexual male population in New York City. The difficulty in making a diagnosis, inadequate therapy, failure to alert potential victims, and official neglect of the epidemic have combined to create a dangerous situation.