Allergic sensitization in asymptomatic children: questioning its innocence
Published: October 22, 2021
At the date this text is published, the “allergy epidemic”, despite hailing back to the 1870’s, seems more present than ever, at least in the Northern Hemisphere where high-pollen season is looming. Type-1 allergy denotes the production of allergen-specific IgE antibodies (allergic sensitization) in the presence of typical symptoms such as rhinitis (“hayfever”) and asthma. The initial reports from the late 19th century of an “epidemic of hayfever” were followed by observations of increases in prevalence of asthma, anaphylactic reactions (allergic shock) and also IgE, once this molecule and its role in allergy were discovered in the late 1960’s.
One recurring topic is to what extent the rise in allergic symptoms and diseases really reflects the prevalence of IgE sensitization, and to what extent sensitized individuals may stay free from clinical symptoms, as the notion of an “epidemic” by nature carries the risk of inflating its importance. One sort of a “push-back” was seen within the Finnish Allergy Programme 2008-2018 where the prevalence of special “allergy diets” in daycare and school settings was nearly halved by requiring objective proof of food allergy. Conversely, methods for detecting IgE have developed from using crude allergens to detection of IgE to hundreds of individual allergenic proteins.
In the current edition of The Journal of Allergy and Clinical Immunology: In Practice, Bunne et al. present data from a longitudinal study of a representative cohort of 1510 Swedish children followed through school age. Skin tests for IgE to airborne allergens and validated questionnaires were deployed at ages 8, 12 and 19 years, with additional blood sampling in a subset to confirm IgE levels. The aim was to examine the impact of age of first detectable IgE sensitization on the subsequent development of asthma and rhinitis.
The earlier IgE to aeroallergens was detected, the greater the risk of subsequent development of rhinitis and/or asthma. At age 19 the prevalence of current rhinitis symptoms was 66% in those sensitized to pollen before age 8, 54% if sensitized between age 8-12 and 36% if sensitized between age 12-19, compared to 15% in never-sensitized. For current asthma and sensitization to animals the corresponding numbers were 29%, 16% and 9%, compared to 6% in never-sensitized. The above pattern was repeated for all studied indices of asthma and rhinitis. When comparing groups, another measure is risk ratio (relative to never-sensitized), which allows for statistically adjusting for other relevant risk factors. After adjustment for demographics, heredity, owning furred pets and maternal smoking, the risk of rhinitis symptoms was ten times higher in those sensitized to pollen before age 8 compared to never-sensitized, with decreasing excess risk the later the individual became sensitized. Asthma indices showed an identical pattern although at lower absolute risk, owing to the multifactorial nature of asthma. Moreover, those sensitized at younger ages had higher levels of IgE and were more commonly sensitized to four or more allergens: 66% had such poly-sensitization at age 19 if sensitized before age 8, compared to 9% if first sensitization occurred between ages 12-19. It thus seems that early sensitization to airborne allergens implicates a more active allergy response entailing higher IgE, sensitization to multiple allergens and high risk for development of allergic symptoms. This is well-known to occur in the more severely allergic patients seen at pediatric allergy clinics for typical features of the allergic march (food allergy, atopic eczema, pre-school wheeze etc). The study by Bunne et al. extends this observation also to the general population, which suggests that healthcare practitioners should keep an eye on their patients where early sensitization is detected, so that later allergic symptoms do not go unnoticed. In the public health domain, the rising secular trends in allergic sensitization in children are a cause for concern, given the high risk of later disease development that the present study clearly shows.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.