Effect of environmental allergen sensitization on asthma morbidity in inner-city asthmatic children

Abstract

Background: Asthma causes significant morbidity in children, and studies have demonstrated that environmental allergies contribute to increased asthma morbidity.

Objective: We investigated the differences between allergen skin tests and specific IgE (SIgE) and the role of IgG in regards to allergen exposure levels, and asthma morbidity in inner-city children.

Methods: Five hundred and six serum samples from the National Cooperative Inner City Asthma Study (NCICAS) were evaluated for SIgE to cockroach (Blattella germanica), dust mite (Dermatophagoides farinae), and Alternaria as well as specific IgG (SIgG) and IgG(4) to cockroach (B. germanica) and total IgE levels. Associations between sensitization to these allergens, exposures, and asthma morbidity were determined.

Results: Sensitization to environmental allergens and total IgE correlated with increased health care and medication use, but not with symptoms of wheeze. Sensitization with exposure to cockroach was associated with increased asthma morbidity, whereas dust mite sensitization was correlated with asthma morbidity independent of exposure. There was also a strong correlation between SIgE levels and skin test results, but the tests did not always agree. The relationship between SIgE and asthma morbidity is linear with no obvious cutoff value. Increased Bla g 1 in the home was a good predictor for sensitization; however, this relationship was not demonstrated for Der f 1. Cockroach SIgG correlated with increased health care use, however, there was no modifying effect of SIgG or SIgG(4) on the association between cockroach SIgE and asthma morbidity.

Conclusions: SIgE levels and skin prick test results to environmental allergens can serve as markers of severe asthma for inner-city children. Asthma morbidity increased in a linear manner with SIgE levels. IgG was not an important predictor or modifier of asthma morbidity.

Figure 1

Relationship between cockroach (Blattella germanica) SIgE level and prick skin test wheal size for cockroach. (mix of American and German cockroach). Also shown are a linear regression line (dark, R²=0.17) and smooth curve (light, R²=0.26) on the original scale and a linear (dark, R²=0.33) and smooth curve (light, R²=0.34) on the log₁₀ transformed cockroach SIgE to illustrate the nonlinear relation on the original scale.

Figure 2

Linear dose-response relationship between SIgE and total IgE with asthma morbidity.

Figure 3

Risk ratios for asthma morbidity parameters by allergen and type of allergy test (specific IgE and prick skin test).

Figure 4

Relationship between level of cockroach-specific IgE and IgG by Bla g 1 exposure. Also shown is the linear regression line. Panel A – Exposure level of <8 U/gram Bla g 1 in the bedroom. Panel B – Exposure level of >8 U/gram of Bla g 1 in the bedroom.