Asthma and lower airway disease
Ascaris, atopy, and exercise-induced bronchoconstriction in rural and urban South African children

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Background

Populations with endemic parasitosis have high levels of IgE but low levels of allergic disease. We investigated the association between infection with the parasite Ascaris allergic sensitization, and exercise-induced bronchospasm (EIB).

Objective

We sought to investigate the effect of Ascaris infection on bronchial hyperreactivity, skin testing, and specific IgE levels.

Methods

A cross-sectional prevalence survey was conducted in urban and rural South African children to measure levels of EIB. A sample of children was enrolled in a nested case-control study for further investigation based on response to exercise. Analyses used weighted logistic regression.

Results

Geometric mean total IgE levels were higher in Ascaris –infected subjects (infected subjects: 451 IU (95% CI, 356-572) vs uninfected subjects: 344 IU (95% CI, 271-437), P = .04), and high levels of total IgE were positively associated with detection of specific IgE to the aeroallergens tested, but there was no significant association between Ascaris infection and titers of specific IgE. Ascaris infection was associated with a decreased risk of a positive skin test response (odds ratio, 0.63; 95% CI, 0.42–0.94; P = .03) but an increased risk of EIB (odds ratio, 1.62; 95% CI, 1.23-2.11; P = .001).

Conclusion

In areas of high parasite endemicity, Ascaris might induce an inflammatory response in the lungs independent of its effect on IgE production. This could explain some of the contradictory findings seen in studies examining the association between geohelminth infection, atopy, and asthma.

Section snippets

Design

The prevalence of EIB was established in a cross-sectional survey of 18 rural schools in Kentani district of the rural Eastern Cape of South Africa and 6 urban schools in Khayelitsha, an informal urban settlement in the Western Cape. Schools in the urban area were contacted in order of construction, starting with the most recently built, and all schools approached agreed to participate in the study. In the rural area all 22 schools within an hour's drive from the study base were approached and

Description of data

The prevalence survey included 1,671 children in rural schools and 1,651 children in urban schools. EIB was identified in 8.7% (n = 146) of rural and 14.9% (n = 246) of urban children. Twelve of the children with positive exercise test results were lost to follow-up. Further examinations were undertaken in 773 children (380 cases and 393 control subjects), 754 consenting to skin prick testing and providing blood samples and 743 providing stool samples. Parents of 696 children (370/436 urban and

Discussion

Ascaris infection was associated with an increased risk of bronchial reactivity and a decreased risk of a positive skin test response. There was no significant association between titers of specific IgE to common airborne allergens and infection with Ascaris. However, Ascaris infection was associated with increased levels of total IgE after controlling for urban environment, and high levels of total IgE were positively associated with detection of specific IgE to the aeroallergens tested. There

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    Supported by a Wellcome Trust Training Fellowship in Tropical Clinical Epidemiology (J.M.C.).

    Disclosure of potential conflict: The authors have declared that they have no conflict of interest.

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