Treatment-ladder and genetic characterisation of parasites in refractory giardiasis after an outbreak in Norway

Objectives: To evaluate the efficacy of a treatment ladder in metronidazole refractory giardiasis, and to compare genetic characteristics of the parasites. Methods: A clinical observational study was carried out in 38 adult patients with metronidazole-refractory giardiasis, during an outbreak in Norway with more than 1200 cases. All patients were treated with albendazole in combination with metronidazole. Those who failed were treated with paromomycin. Those who failed on paromomycin were treated with quinacrine in combination with metronidazole. Giardia isolates from 17 patients were characterised by PCR and sequencing at two separate genes. Results: Metronidazole in combination with albendazole was effective in 30 (79%) out of 38 patients. Paromomycin was effective in three out of six patients. Quinacrine in combination with metronidazole was effective in 3 patients. Molecular characterisation of the Giardia isolates revealed that these parasites were identical at two different gene segments, while sequence profiles from isolates at the peak of the outbreak were more heterogenous.