Original Articles
The prevalence of contact allergy differed between population-based and clinic-based data

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Abstract

Objective

Epidemiologic evidence on contact allergy (CA) largely relies on clinical studies. However, the effects of the selection process until consultation as patient are largely unclear.

Study design and setting

Prevalences of contact allergy to important allergens estimated from the population-based nested case–control study “KORA Allergy Study” in Augsburg, Germany (a subsample from the third MONICA survey in 1997/1998, n = 1141), were compared with proportions found in the Department of Dermatology of the Augsburg Municipal Hospital in patients of similar age patch tested between 1997 and 2000 (n = 555). Prevalences were standardized for sex, age, and atopic dermatitis as potential confounders.

Results

Among the 25 substances tested, the fragrance mix (MONICA, estimated from the KORA Allergy Study: 11.4%, hospital: 12.9%) and nickel (MONICA: 9.9%, hospital: 12.9%) were the most common allergens. Larger differences between prevalences were noted particularly with ingredients of topicals used to treat varicose ulcers—a speciality of the Augsburg department, which is also reflected by comparing the department with the whole Information Network of (n =40) Departments of Dermatology (IVDK).

Conclusion

This locally matched comparison illustrates the differential effect of selection until presentation in dermatological departments.

Introduction

Contact allergy (CA), a pathologic response after—usually repeated—contact to environmental substances of low molecular weight occurring in a varying proportion of exposed persons, often results in clinical disease, that is, allergic contact dermatitis (ACD), which can be disabling. CA is diagnosed by patch testing, a technique of controlled exposure of patients suspected to have ACD to a standardized set of substances frequently found to be the cause of ACD. Patch testing has also been applied to different population samples to estimate the prevalence of CA in general (e.g., “contact allergy to at least one substance of a standard panel”), and specific CA (i.e., CA to a certain substance, like nickel, fragrances, etc.), respectively, which was found surprisingly high [1], [2]. At the same time, different questionnaire-based surveys found a high prevalence of symptoms compatible with ACD—albeit not being able to verify this by patch testing—and of a doctor's diagnosis “ACD,” respectively [3], [4]. Thus, CA and its clinical manifestation, ACD, can be regarded as a relevant public health problem.

However, as only very few specific CAs are truly frequent on a population level, the elucidation of risk factors for the bulk of specific CAs largely relies on the analysis of patients patch tested because of suspected ACD [5]. Obviously, such studies cannot directly estimate morbidity, as the selection process of a person with ACD until presentation in a dermatologic department cannot easily be operationalized to derive population-adjusted morbidity estimates.

The present study compares population-based estimates of specific CAs recently obtained in the KORA Allergy Study (based in Augsburg as a subsample of the third MONICA survey) [6] with prevalences found in patients of the local Department of Dermatology and Allergology (Augsburg Hospital), which is a member of the Information Network of Departments of Dermatology (IVDK) surveillance network, and furthermore, with prevalences found in the whole IVDK network during the period 1997–2000. This comparison provides some insight into the effects of selection processes as outlined above. To our knowledge, only one such comparison has yet been performed [7].

Section snippets

Methods

The population-based study platform KORA (“Study Platform for Cooperative Health Research in the Region of Augsburg,” http://www.gsf.de/KORAN/en), the KORA Allergy Study [6] and the surveillance system IVDK [5] have been described in detail; the following sections will summarize information essential for the understanding of our article. Both studies followed standard international guidelines for the application and interpretation of patch test results [8], and applied the same patch test

Results

Between January 1997 and December 2000, 555 patients were patch tested in the Department of Dermatology and Allergology of the Augsburg Central Hospital. During the same period, 39,050 patients were patch tested in the whole IVDK.

Demographic data is given in Table 1, including the “MOAHLFA-index” [12] as far as this data was available, comparing the KORA sample, the Augsburg hospital patients, and the entire IVDK group of patch test patients. Some characteristics of the KORA Allergy Study are

Discussion

CA is a common condition on a population level. This has previously been reported from Denmark [1], [7], [13], based on different cross-sectional samples, and recently from Germany for an adult sample of the general population [6]. Although ACD resulting from a specific CA is only very rarely a fatal disease, its impact must not be underestimated, both on a complex individual scale of quality of live, and socioeconomically, for example, due to work absenteeism. Thus, improved prevention is an

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