Associated positive patch test reactions to standard contact allergens: 10-year data from the Slovenian E-Surveillance System

Background A considerable share of patients tested with a baseline patch test series respond with a positive reaction to more than one allergen, and some associations between synchronous positive reactions to distinct baseline patch allergens have been described in the literature. Objectives To evaluate the prevalence of sensitization to haptens of the European baseline series as well as the prevalence of oligosensitization and polysensitization and the most significant associated positive patch test reactions in Slovenia. Methods Patch testing data collected by the Slovenian E-Surveillance System from January 2008 to December 2017 were retrospectively analysed. Results Of a total of 15 171 patients analysed, 39.29% showed at least one positive reaction. The highest prevalences were noted for metals (nickel[II]sulfate hexahydrate: 16.33%) and fragrances (fragrance mix I: 6.70%). The correlation analysis showed the strongest correlation between mercapto mix and 2-mercaptobenzothiazole (61.2%), fragrance Mix II and hydroxyisohexyl 3-cyclohexene carboxaldehyde (50.5%), and potassium dichromate and cobalt(II) chloride hexahydrate (33.3%). Conclusions Sensitization prevalences to the most common haptens were described, and their strongest correlations on a national level quantified. A comparison with other European results confirms already known associations between allergens in terms of cross-reactivity.