Furthermore, the infection seems to spark an increased risk of having both conditions at the same time, prompting the authors to suggest that "the long term clinical consequences of Giardia may be more severe than previously thought."
Giardia lamblia is a parasite that is found on every continent. It is a common source of acute and longer term gut infection, and frequently implicated in travellers’ diarrhoea in tropical and subtropical areas, particularly where hygiene is poor.
It is mainly spread through contaminated drinking water, but it can also be passed on through person to person contact. It had been thought that once treated, it did not cause any long term problems.
The researchers tracked the health of 817 local residents who had become infected with Giardia in 2004 and over 1,000 healthy people, matched for age and sex, for a period of three years. The source of the infection was contaminated water from a reservoir in Bergen, Norway.
They found that the prevalence of irritable bowel syndrome (IBS) was significantly higher in those who had had the infection. These people were more than three times as likely to have persistent IBS, after taking account of factors likely to unduly influence the results.
They were also four times as likely to have chronic fatigue symptoms.
What’s more, the researchers found that the likelihood of having both conditions together was almost seven times as high among those who had had the infection.
Normally, the prevalence of IBS and chronic fatigue tends to be higher in women, but there was no evidence of a gender bias among the study participants.
Giardia infection is not endemic in Norway, and the researchers caution that their findings may not be applicable to countries outside the developed world: further research would be needed before such conclusions could be drawn.