Giardia Linked to Long-term Risk for IBS, Chronic Fatigue

Jennifer Garcia

August 20, 2014

Infection with Giardia may triple the risk for irritable bowel syndrome (IBS) and chronic fatigue (CF) even years after infection, according to a prospective study published online August 12 in the journal Clinical Infectious Diseases.

Kurt Hanevik, MD, PhD, from the University of Bergen, Norway, and colleagues identified 1252 individuals diagnosed with Giardia infection during an outbreak in 2004 and followed them for the 6 years after infection. They compared data from the Giardia-exposed group with data from 2504 individuals who were matched for age and sex; the researchers identified control participants through Statistics Norway in 2007.

Of those participants, 748 (60.4%) participants in the exposed group and 878 (35.9%) in the control group responded to questionnaires mailed in 2007 and 2010;

The questionnaires asked about participants' health and daily activities. All individuals with giardiasis were treated, and polymerase chain reaction testing of stool samples among exposed individuals 5 years later was negative. The researcher group published the results of the 3-year follow-up previously.

Six years after the Giardia outbreak, the prevalence of Rome III–defined IBS was 39.4% (291/739) among patients in the exposed group compared with 11.6% (101/870) among those in the control group (relative risk [RR], 3.4; 95% confidence interval [CI], 2.9 - 3.9).

The prevalence of CF was 30.8% (226/733) in the exposed group compared with 11.0% (96/874) among the control group (RR, 2.9; 95% CI, 2.3 - 3.4).

The researchers calculated that 65% (95% CI, 57.3% - 70.8%) of the CF cases in the exposed group could be attributed to past Giardia infection, as could 70.5% (95% CI, 65.1% - 74.6%) of the IBS cases.

"The main finding in this study was the high prevalence of chronic fatigue (30.8%) and irritable bowel syndrome (39.4%) six years after laboratory confirmed giardiasis and that these two conditions were strongly associated," write Dr. Hanevik and colleagues.

Evaluation of a large population of exposed individuals during an outbreak "made it possible to study the natural course of IBS and CF after giardiasis, and shows a significantly increased risk for both IBS and CF even six years after the infection," the authors write.

Despite a decrease in the prevalence of both conditions in the exposed group (15.3% decrease for CF and 6.7% decrease for IBS) between the 2007 and 2010 questionnaires, the researchers found that both conditions were more persistent over time in the exposed group compared with the control group.

Using a logistic regression model that included sex, age, and Giardia exposure, the researchers found the Giardia exposure was significantly associated with both persistent CF (RR, 2.13; 95% CI, 1.55 - 2.64) and persistent IBS (RR, 1.64; 95% CI, 1.29 - 1.95). Increasing age was also found to be a risk factor for persistent CF.

The authors acknowledge study limitations such as the possibility of selection bias and the possibility that risk for disease may have been overestimated because of differences among the control and exposed groups.

"[B]ased on our findings, Giardia induced IBS and/or CF could be considered a differential diagnosis, especially in returning travelers who present with such symptoms and where infectious microorganisms are not detected," Dr. Hanevik and colleagues conclude.

Funding for this study was provided by the Norway Regional Health Authority and the University of Bergen. The authors have disclosed no relevant financial relationships.

Clin Infect Dis. 2014. Published online August 12, 2014. Full text

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