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Original article
Irritable bowel syndrome and chronic fatigue 3 years after acute giardiasis: historic cohort study
  1. Knut-Arne Wensaas1,2,
  2. Nina Langeland3,
  3. Kurt Hanevik3,4,
  4. Kristine Mørch4,5,
  5. Geir Egil Eide1,6,
  6. Guri Rortveit1,2
  1. 1Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway
  2. 2Research Unit for General Practice, Uni Health, Bergen, Norway
  3. 3Institute of Medicine, University of Bergen, Bergen, Norway
  4. 4National Centre for Tropical Infectious Diseases, Haukeland University Hospital, Bergen, Norway
  5. 5Department of Medicine, Unit for Infectious Diseases, Haukeland University Hospital, Bergen, Norway
  6. 6Centre for Clinical Research, Haukeland University Hospital, Bergen, Norway
  1. Correspondence to Dr Knut-Arne Wensaas, Research Unit for General Practice, Uni Health, Kalfarveien 31, N-5018 Bergen, Norway; knut-arne.wensaas{at}


Background Giardia lamblia is a common cause of gastroenteritis worldwide, but there is limited knowledge about the long-term complications.

Objective To estimate the relative risk of irritable bowel syndrome (IBS) and chronic fatigue 3 years after acute giardiasis.

Design Controlled historic cohort study with 3 years' follow-up. Data collected by mailed questionnaire.

Setting Waterborne outbreak of giardiasis in the city of Bergen, Norway.

Participants 817 patients exposed to Giardia lamblia infection verified by detection of cysts in stool samples and 1128 matched controls.

Main outcome measures IBS and chronic fatigue.

Results The prevalence of IBS in the exposed group was 46.1%, compared with 14.0% in the control group, and the adjusted RR=3.4 (95% CI 2.9 to 3.8). Chronic fatigue was reported by 46.1% of the exposed group and 12.0% of the controls, the adjusted RR was 4.0 (95% CI 3.5 to 4.5). IBS and chronic fatigue were associated and the RR for the exposed group of having a combination of the two outcomes was 6.8 (95% CI 5.3 to 8.5). The RR was also increased for having just one of the two syndromes, 1.8 for IBS (95% CI 1.4 to 2.3) and 2.2 for chronic fatigue (95% CI 1.7 to 2.8).

Conclusions Infection with Giardia lamblia in a non-endemic area was associated with a high prevalence of IBS and chronic fatigue 3 years after acute illness, and the risk was significantly higher than in the control group. This shows that the potential consequences of giardiasis are more serious than previously known. Further studies are needed, especially in areas where giardiasis is endemic.

  • Giardia lamblia
  • giardiasis
  • functional gastrointestinal disorders
  • irritable bowel syndrome
  • chronic fatigue disorder
  • parasitic diseases
  • infectious disease
  • biostatistics

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  • Funding An open grant from the Municipality of Bergen covered the cost for production and mailing of the questionnaire and for the services delivered by Statistics Norway. KAW was partly funded by the Norwegian Medical Association's Funds for Research in General Practice. All researchers are independent from the sponsors. The sponsors had no role in study design, in collection, analysis and interpretation of data, or in writing or deciding to submit the manuscript.

  • Competing interests All authors have completed the Unified Competing Interest form at (available on request from the corresponding author) and declare that except for the information stated about funding no authors (1) have received support from any organisation for the submitted work, (2) have any financial relationships with any organisations that might have an interest in the submitted work in the previous 3 years, or (3) have any other relationships or activities that might appear to have influenced the submitted work.

  • Ethics approval This study was approved by the Regional Committee for Medical and Health Research Ethics (project 150.07), and by the Ombudsman for Privacy in Research, Norwegian Social Science Data Services (project 17014).

  • Provenance and peer review Not commissioned; externally peer reviewed.