Intestinal protozoa in homosexual men of the San Francisco Bay area: prevalence and correlates of infection.

To compare the prevalence of intestinal parasitic infection in male homosexuals selected from other sources with the levels previously reported from clinic-derived populations, various homosexual groups of the San Francisco Bay Area were checked by means of stool examination and questionnaires for prevalence of intestinal parasites and for related sexual behavioral patterns during a 3-year period. The prevalence of Entamoeba histolytica (28.6%) was similar to that reported in other studies, whereas that of Giardia lamblia was lower. Infection with E. histolytica was correlated significantly with a prior history of syphilis or gonorrhea (P less than 0.0001), with the number of sexual partners in the preceding 12-month period (P less than 0.0001), and with the reported frequency of oral-anal sexual contact (P less than 0.001). Giardial infection was also significantly related to oral-anal sex (P less than 0.001). No relation was seen between the presence or absence of gastrointestinal symptoms and infection with pathogenic protozoa. Factors associated with parasitic infection differed little from those found in previous studies, although significance levels were considerably higher because of the larger size of our study group.