Relationship of patch test positivity in a general versus an eczema population

Using previously generated data from multicenter studies European Environmental and Contact Dermatitis Research Group (EECDRG) and North American Contact Dermatitis Group (NACDG), we compare patch test positivity of random sample and eczema populations, attempting to ascertain how one might extrapolate frequency from an eczema group to a general population. We included population-based mathematical estimates for patch test reaction in the general population using the Multinational MONItoring of trends and determinants in Cardiovascular disease MONICA and Clinical Epidemiology and Drug-Utilization Research (CE-DUR) systems. Data analysis provides a ratio of eczema population:random sample population for each allergen and an overall ratio of all allergens 5:1 for actual data and 6:1 for population-based estimates (according to the MONICA and CE-DUR systems). If the positivity rate were the same in each population, the ratio would approximate 1. The individual allergen ratios ranged from formaldehyde at 11.6 to parabens at 1.0, with respect to the NACDG. Some differences may be explained by exposure (neomycin) being greater in patients than in random population. Materials of ubiquitous exposure - i.e. fragrance mix and nickel - had ratios closer to 1. Taken together, data obtained in eczema patients may be viewed as part of a complex biology and may eventually be of use in aiding validation of predictive dermatotoxilogic assays and in public health assessments.