Objective: Bacterial overgrowth has been implicated in the pathogenesis of irritable bowel syndrome (IBS). The objective of this study was to investigate whether post-infectious IBS following Giardia lamblia infection is related to intestinal bacterial overgrowth, as diagnosed by the lactulose breath test (LBT).
Material and methods: Seventy-seven patients with persistent gastrointestinal complaints related to a recent outbreak of G. lamblia infection were included in the study. Despite one or several courses of treatment with metronidazole during the previous months, 23 of the patients were still stool positive for G. lamblia, whereas the remaining 54 patients had cleared the infection. All patients and 42 healthy volunteers underwent a LBT with 10 g lactulose, and their customary and post-LBT abdominal symptoms were scored.
Results: Ninety-five percent of the patients had IBS. Lactulose-induced hydrogen breath excretion was not significantly different in patients and controls. Customary and post-LBT symptoms were abnormally high in the patients, irrespective of both G. lamblia infection status and LBT results. Furthermore, lactulose challenge replicated the patients' customary complaints in 70% of the patients.
Conclusions: Gastrointestinal complaints in patients with persistent or cleared giardiasis were unrelated to hydrogen breath excretion after lactulose challenge. Post-giardiasis IBS cannot be ascribed to intestinal bacterial overgrowth, as diagnosed by LBT.