Prevalence of patch test results from 1970 to 2002 in a multi‐centre population in North America (NACDG)

Abstract

The North American Contact Dermatitis Group (NACDG) has members who assess subjects with suspected allergic contact dermatitis (ACD) and patch tests them with the same screening allergens using a standardized procedure permitting analysis of long-term trends in patch test reactions. This study reports the trends in prevalence patch test positivity of allergens by pooling data collected by the NACDG between 1970 and 2002. Patients were tested with the screening series of allergens, using a standardized technique. Data from these patients were recorded on a standard computer entry form and analysed. More than 100 allergens were tested on over 34,000 patients during several patch studies between the period. The Cochran-Armitage test of trend is used to evaluate changes in prevalence over time. 4 trends are noticed: (1) The incidence of presumed allergic nickel (P < 0.0001) and quaternium-15 (P < 0.0001) reactions rose with consistency over the years. (2) While that of cinnamic aldehyde (P = 0.21) and p-phenylenediamine (P < 0.0001) decreased. (3) The prevalence of positive reactions for potassium dichromate (P < 0.0001) shows an initial steady decrease but then a sharp increase starting from the 1996 period. (4) In contrast, thiuram (P = 0.0008) and neomycin (P < 0.0001) show an initial general increase, with a sharp decrease between 1998 and 2002. Implications for opportunities to prevent ACD by utilizing less-allergenic alternatives appear robust; however, we do not wish to over generalize interpretations because of important limitations.