Intestinal protozoa in homosexual men in Edinburgh

Our objective was to determine the prevalence of intestinal protozoa in homosexual men attending a sexually transmitted diseases (STD) clinic, to compare it with the prevalence in a previous study from the same clinic, and to examine the relationship, if any, between the presence of protozoa and sexual practices. Men who consecutively attended the clinic and who gave a history of having had recent sexual contact with another male were invited to provide a stool sample for protozoological examination. Diarrhoeal samples were examined by direct microscopy for trophozoites and cysts and, after staining, for Cryptosporidium spp. In all cases, a modified formol-ether method was used to concentrate protozoal cysts before microscopy. One hundred and seventy-five of the 257 men invited to participate in the study provided a stool sample. At least one species of protozoan was found in 99 (57%) men. Giardia intestinalis was identified in only 5 (3%) men. Blastocystis hominis was found in 46 (26%) men, but the presence of this protozoan was not associated with diarrhoea. Other than the prevalence of Entamoeba dispar/histolytica and G. intestinalis, which remained unchanged, the proportion of men who harboured the non-pathogenic protozoa was significantly increased from 1981/82. A correlation between oral-anal sex or peno-insertive or peno-receptive anal intercourse and the prevalence of protozoa was not found. There was also no correlation between the number of species of protozoa carried and these sexual practices. The presence of protozoa was not associated with a history of foreign travel or sexual contact with a man who had recently travelled outside the UK. The study showed that, although the prevalence of infection is low, giardiasis is still transmissible amongst homosexual men. A correlation between individual sexual practices and the prevalence of intestinal protozoa was not found.