Crohn's disease is frequently complicated by giardiasis.

Giardiasis is a common infection, and many of its symptoms are similar to those of Crohn's disease. Despite a long discussion on the role of microbiologic agents in Crohn's disease, giardiasis has never been investigated. We studied giardiasis as assessed by the occurrence of cysts in 86 patients with Crohn's disease, in 82 patients with other gastrointestinal disease, and in 52 patients without gastrointestinal disease. In addition, in 20 patients with Crohn's disease the effects of metronidazole on giardiasis and disease activity were studied. Frequency of giardiasis was 61.6% in patients with Crohn's disease, 31.7% in patients with other gastrointestinal disease, and 5.8% in the control group (p less than 0.01). Stool frequency, disease activity, and humoral signs of inflammation in patients with Crohn's disease showed no relationship to giardiasis. All but two patients treated with metronidazole became free of cysts. Crohn's disease activity index decreased in 14 of 20 patients (p less than 0.05). In conclusion, giardiasis is a common finding in patients with Crohn's disease. Treatment of giardiasis can, in individual cases of Crohn's disease, result in a quick recovery from symptoms of high disease activity.