Markers of Microbial Exposure Lower the Incidence of Atopic Dermatitis

The hygiene hypothesis suggests that reduced exposure to infectious agents in early life contributes to increase of allergic disease. This study directly evaluated the impact of early microbial exposure and the onset of atopic disease.

Children between the ages of 3–24 months were enrolled between March 2011 and April 2016 from 10 Italian centers. Study subjects were children with first-time diagnosis of atopic dermatitis (AD) during the enrollment visit. Controls were of the same age presenting to dermatology clinic without diagnosis of AD.

This was a matched case-control study on the impact of exposure to infectious agents on the incident of AD. 426 cases with a first diagnosis of AD were matched to 426 children attending a pediatric/dermatological clinic for a non-atopic disorder. The time elapsed between markers of microbial exposure and disease onset was noted and compared with controls with the same time period of exposure from birth as matched cases. Odds ratios (OR) were calculated using multivariable logistic regression models according to age, sex, and period of enrollment, and including confounders of parental history of allergy, having siblings, indoor pets, duration of breastfeeding, and having ≥4 infections.

66% of enrolled children were males. 52% of children were 3–6 months of age with 21% 12 months or age or older. 84% of children had their first AD symptoms not more than 3 months before enrollment. Severity of AD in cases as measured by SCORAD scale had a mean of 49.7 with SD of 17.2. Several factors showed protective effect for developing AD. For children with ≥4 infections compared with no infections the adjusted OR of AD first occurrence was 0.35 (95% CI, 0.13–0.95; P value .39). When evaluating the severity of infections, only episodes resulting in fever >38.0°C and not treated with antibiotics showed protection. There was a decreasing trend in risk observed with increasing number of siblings. For 2 or more siblings, the adjusted OR was 0.62 (95% CI, 0.39–0.99; P value .048) for first occurrence of AD. Daily contact with dogs was inversely associated with AD risk with adjusted OR of 0.4 (95% CI, 0.22–0.75; P value .004). This was not observed with daily cat exposure.

Direct and indirect markers of microbial exposure to include more frequent infections, having siblings, and contact with dogs are associated with lower risk of AD first occurrence in young children.

These authors took a unique look at determining the influence of early life exposure to microbes on the atopic state by using a large case-control study. They also attempted to analyze simultaneously many different cofactors which could contribute to direct or indirect microbial exposure. This adds additional data of how early life exposure plays a role in the development of atopy as suggested by the hygiene hypothesis.