In patients with persisting symptoms after metronidazole treated Giardia infection we commonly found chronic Giardia infection and microscopic duodenal inflammation, especially in illness duration less than 7 months. Both these findings subsided over time. Increasingly, investigations could not determine a definite cause for the persistent symptoms. The very long-term post-giardiasis diarrhoea, bloating, nausea and abdominal pain documented here need further study.

During the autumn and winter of 2004 and 2005, an extensive outbreak of waterborne giardiasis occurred in Bergen, Norway. Over 1,500 patients were diagnosed with giardiasis. Analysis of water from the implicated source revealed low numbers of Giardia cysts, but the initial contamination event probably occurred up to 10 weeks previously. While sewage leakage from a residential area is now considered to be the probable source of contamination, during the episode waste from one particular septic tank was thought to be a possible source. Genotyping of cysts from the septic tank demonstrated that they were assemblage A cysts, although the sequences were not identical to any previously published sequences. For the ␤-giardin gene, the closest published subgenotype was subgenotype A3; for the gdh gene, the closest published subgenotype was subgenotype A2. Genotyping of cysts from 21 patient samples revealed that they were assemblage B cysts; thus, the septic tank was unlikely to be the contamination source. Sequencing of the ␤-giardin and gdh genes from patient samples and a comparison of the sequences gave complex results. For the ␤-giardin gene, three isolates had sequences identical to subgenotype B3 sequences. However, other isolates had between one and four single-nucleotide polymorphisms (SNPs). For the gdh gene, none of the sequences were identical to the sequence published for subgenotype B3, and the sequences had between one and three SNPs. One isolate, which was identical to subgenotype B3 at the ␤-giardin gene, was more similar to subgenotype B2 at the gdh gene. Grouping the isolates on the basis of SNPs resulted in different groups for the two genes. The results are discussed in relation to giardiasis in Norway and to other Giardia genotyping studies.Human parasitic infections, although probably underdiagnosed, are considered to be rare in Norway. Giardiasis is a reportable infection, and the annual recorded occurrence is 300 to 400 cases (around 8 cases per 100,000 population) for the whole country (6).During the autumn and winter of 2004 and 2005, an extensive outbreak of waterborne giardiasis occurred in Bergen, Norway (Table 1). Over 1,500 patients were laboratory diagnosed with Giardia infection, although considerably more individuals had symptoms, and Giardia infections considered to be outbreak associated continued to be diagnosed until June 2005.This was the first outbreak of a waterborne parasitic disease recorded in Norway, and various details were published in a report by the local council and members of the Norwegian Food Safety Authority (10). Once the increase in giardiasis cases had been noted, geographic clustering of the cases rapidly made it apparent that the outbreak was probably waterborne, and a particular water source was implicated.The initial source of contamination of the water supply was obviously of concern and interest, not least to ensure that repeat contamination events did not occur. The final report (10) indicates that sewage leakage from a residential area with drainage towar...

Albendazole and quinacrine both in combination with metronidazole were effective in treating metronidazole-refractory giardiasis in this cohort. Paromomycin was less effective. Particular Giardia sub-genotypes may have been associated with the treatment-refractory giardiasis in these patients, although other undefined factors are probably also of importance.

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.