Entamoeba histolytica cyst passers: clinical features and outcome in untreated subjects

To examine whether Entamoeba histolytica is the cause of a variety of intestinal disorders, as often implicated, a two-part study was conducted. In part 1, 184 patients attending a gastroenterology clinic and needing a sigmoidoscopy had a rectal biopsy specimen and a stool sample cultured for E histolytica. Part of the biopsy specimen was examined histologically. In addition, serum was tested for antibody to E histolytica. 34 (18.7%) patients were culture positive. There was no correlation between the culture results and patients' symptoms except for diarrhoea, which was more common in the culture-negative group, or with histological or serological findings. In the second part of the study, 15 culture-positive patients were followed up untreated for a mean (+/- SD) of 8.6 (+/- 4.9) months, range 1-18. In all 15 patients spontaneous eradication of the parasite occurred, and in none did symptoms of invasive amoebiasis develop. Thus E histolytica seems not to be responsible for many of the bowel complaints commonly attributed to it. In these cyst passers the cysts are probably incidental to an irritable bowel syndrome or some other organic disease. There seems to be little justification for treating cyst passers since eradication of the parasite occurs spontaneously and the danger of invasive amoebiasis is negligible. Such a practice would result in an enormous saving on the cost of drugs.