Childhood helminth exposure is protective against inflammatory bowel disease: a case control study in South Africa

Inflammatory bowel disease (IBD) is more common in countries with improved hygiene, suggesting that environmental exposures may be associated with its development. The primary objective of this study was to examine the association between self-reported childhood helminth infection and the development of IBD in South Africa.

Unmatched case-control study. Logistic regression was used to model associations with IBD.

There were 88 patients with Crohn's disease (CD), 63 with ulcerative colitis (UC), and 219 control subjects. Of the 151, 93 (61.6%) IBD subjects (35 of 63 [55.6%] had UC and 58 of 88 [65.9%] had CD) reported childhood helminth exposure compared with 200 of 219 (91.3%) non-IBD subjects (P < 0.001). Helminth infection (adjusted odds ratio [AOR] = 0.2; 95% confidence interval [CI], 0.1-0.4), shared housing (AOR = 0.1; 95% CI, 0.04-0.4), and raw beef consumption (AOR = 0.2; 95% CI, 0.1-0.6) were protective, whereas urban dwelling (AOR = 4.2; 95% CI, 2.0-8.8) and parental tertiary education (AOR = 18.2; 95% CI, 3.2-103.7) were associated with CD. Helminth infection (AOR = 0.2; 95% CI, 0.1-0.6), mixed race (AOR = 0.1; 95% CI, 0.03-0.5), smoking (AOR = 0.2; 95% CI, 0.07-0.5), shared housing (AOR = 0.1; 95% CI, 0.01-0.4), and raw beef consumption (AOR = 0.1; 95% CI 0.04-0.5) were protective against UC, whereas parental tertiary education (AOR = 12.7; 95% CI, 1.0-157.4) was associated with UC.

This study demonstrates a protective association of childhood helminth infection against the development of IBD and supports the "hygiene hypothesis" that improved living conditions may increase the incidence of IBD. Our epidemiologic conclusions provide support that helminths may have immunomodulatory effects which provides protection against the development of IBD later in life.