Colonization with the Staphylococcus aureus bacterium was significantly and independently associated with food allergy in young children with eczema enrolled in a pivotal peanut allergy prevention study.
S.aureus is a marker for severe eczema, and early eczema is a widely recognized risk factor for developing food allergies in young children.
But the findings from the Learning Early About Peanut Allergy (LEAP) study cohort show that even after controlling for eczema severity, skin S. aureus positivity was associated with an increased risk for developing allergies to peanuts, eggs, and cow’s milk.
S. aureus colonization was also associated with persistent egg allergy until at least age 5 or 6 years in the LEAP cohort analysis in the Journal of Allergy and Clinical Immunology.
The lead researcher, Olympia Tsilochristou, MD, of Kings College London, said in a press statement that the findings could help explain why young children with eczema have a very high risk for developing food allergies. While the exact mechanisms linking the two are not known, “our results suggest that the bacteria Staphylococcus aureus could be an important factor contributing to this outcome,” she said.
The findings also suggest that S. aureus colonization may inhibit peanut tolerance among at-risk infants when peanuts are introduced very early in life.
Among the nine participants in the peanut-consumption arm of the study (i.e., no peanut allergy at baseline) who had confirmed peanut allergy at 60 and 72 months, all but one were colonized with S. aureus at one or more LEAP study visits.
“The fact that S. aureus was associated with greater risk of peanut allergy among peanut consumers but not peanut avoiders further suggests that peanut consumption was less effective in the prevention of peanut allergy among participants with S. aureus compared with those with no S. aureus,” the researchers wrote.
The LEAP study enrolled infants ages 4-11 months with severe eczema, egg allergy, or both. The babies were randomized to therapeutic peanut consumption or peanut avoidance, and all had eczema clinical evaluation and culture of skin and nasal swabs at baseline.
The follow-up LEAP-On study assessed the children at age 72 months, after 12 months of peanut avoidance in both groups.
Skin and nasal swabs were obtained at baseline and at age 12, 30, and 60 months. A total of 48.8% of the participants had some form of S. aureus colonization (32.2% skin and 32.3% nasal) on at least one LEAP study visit, with most having just one positive test result. The greatest rates of colonization were recorded at 4-11 months of age.
S. aureus colonization was significantly associated with eczema severity, along with hen’s egg white and peanut specific immunoglobulin (sIg)E production at any LEAP visit. But even after controlling for eczema severity, hen’s egg white and peanut sIgE levels at each LEAP and LEAP-On visit were significantly associated with skin S. aureus positivity, the team noted.
“This relationship was even stronger when we looked into high-level hen’s egg white and peanut sIgE production,” the researchers wrote. “Similar findings were noted for cow’s milk, where high-level sIgE production to milk at 30, 60, and 72 months of age was related to any skin S. aureus colonization. Together, these data suggest that S. aureus is associated with hen’s egg, peanut, and cow’s milk allergy.”
In the LEAP study, very early peanut consumption was found to reduce the risk of peanut allergy at 60 months in infants at high risk for developing the allergy, but infants in the consumption arm of the study with S. aureus colonization were approximately seven and four times more likely to have confirmed peanut allergy at 60 and 72 months, the team said.
Study strengths, Tsilochristou and co-authors noted, included the rigorous design; a limitation was the reliance on bacteriological culture to identify S. aureus colonization rather than using DNA-based testing.
“S. aureus has been implicated in the development and severity of atopic diseases, namely eczema, allergic rhinitis, and asthma; our findings extend these observations to the development of food allergy independent of eczema severity,” the investigators concluded.
“The role of S. aureus as a potential environmental factor should be considered in future interventions aimed at inducing and maintaining tolerance to food allergens in eczematous infants. Further prospective longitudinal studies measuring S. aureus with more advanced techniques and interventional studies eradicating S. aureus in early infancy will help elucidate its role in the development of eczema or food allergy,” the team wrote.
Funding for the research was provided by the National Institute of Allergy and Infectious Diseases (NIAID), the Medical Research Council & Asthma U.K. Centre, the U.K. Department of Health, and others.
Tsilochristou reported receiving grants from the Clemens von Pirquet Foundation during the conduct of the study; the study’s principal investigator reported receiving grands from the NIAID, the U.K. Food Standards Agency, Food Allergy Research & Education, the U.K. Department of Health, and the National Peanut Board.