European Surveillance System on Contact Allergies (ESSCA): polysensitization, 2009-2014.

Background: Polysensitization, defined as being allergic to three or more haptens from the European baseline series, is considered to reflect increased susceptibility to developing a contact allergy, and is likely to be associated with an impaired quality of life.

Objectives: To evaluate the prevalences of polysensitization across Europe and to analyse factors associated with polysensitization.

Methods: Patch test data collected by the European Surveillance System on Contact Allergies (ESSCA; www.essca-dc.org) in consecutively patch tested patients from January 2009 to December 2014, comprising 11 countries and 57 departments, were retrospectively analysed.

Results: A total of 86 416 patients were available for analysis, showing a standardized prevalence of polysensitization of 7.02%, ranging from 12.7% (Austria) to 4.6% (Italy). Allergen pairs with the strongest association are reported for the total population, for South Europe, and for North/Central Europe. Overall, polysensitized patients showed a higher percentage of extreme (+++) positive patch test reactions than oligosensitized patients. Female sex, occupational dermatitis and age > 40 years were risk factors for polysensitization.

Conclusions: The varying prevalences of polysensitization across Europe most likely reflect differences in patient characteristics and referral patterns between departments. Known risk factors for polysensitization are confirmed in a European dermatitis population.