Giardia lamblia infections become clinically evident by eliciting symptoms of irritable bowel syndrome.

Abstract

Giardia lamblia infection is often asymptomatic. Its main, but not well understood, symptom is diarrhea. An outbreak of giardiasis in our town allowed us to test the hypothesis that patients with symptomatic infection are, actually, patients with Irritable Bowel Syndrome (IBS) exacerbated by giardiasis. We studied 100 patients with symptomatic giardiasis. Eighty-two of them were also affected by IBS, according to the "Rome 1992 Criteria". They were randomized in four groups, two of which (A and B), made up of 41 patients each, included the subjects with giardiasis and IBS, whereas the remaining two (C and D), made of up of 9 patients each, included subjects with giardiasis only. The groups A and C were treated with metronidazole, whereas groups B and D were treated with drugs commonly used for IBS, but inactive against the parasite. According to a single blind protocol, the treatment with metronidazole was ineffective in the groups with giardiasis and IBS. Instead, the treatment for IBS ameliorated the symptoms in these patients. On the contrary, the groups without IBS improved only with metronidazole. The large majority of patients with symptomatic giardiasis are affected by IBS and are not cured by antiparasite treatment.