Treatment-refractory giardiasis is predominantly an imported infection from South Asia associated with Giardia sub-assemblage BIII: a five-year study from the Czech Republic

• This study confirms the limited efficacy of metronidazole treatment of giardiasis. • The most frequently diagnosed Giardia genotype in Czechia is assemblage B. • Travellers from South Asia are at significantly higher risk of treatment failure. • Treatment outcome and/or genotype are not associated with any specific symptoms. Giardiasis is a cosmopolitan parasitic infection caused by a protozoan pathogen Giardia intestinalis . A high number of failures complicates the metronidazole (MTZ) treatment. However, long-term studies characterising the parasites associated with MTZ treatment failures are lacking. This study was designed to map Giardia genotypes, clinical manifestations and geographical origin of giardiasis in a patient cohort from the Czech Republic. A multilocus genotyping was applied to 93 Giardia DNA isolates collected over five years in a tertiary care hospital diagnostic facility, and corresponding patient data, including the treatment outcomes, were evaluated. We found that treatment refractory giardiasis (32.9% of infections) was always symptomatic, associated with South-Asian origin and caused mainly by sub-assemblage BIII parasites. This study confirms the limited efficacy of MTZ treatment, especially in travellers returning from South Asia.