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

Background: 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.

Objective: This study reports the trends in prevalence patch test positivity of allergens by pooling data collected by the NACDG between 1970 and 2002.

Patients/methods: 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.

Results: 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.

Conclusion: 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.