Background: Patch testing is the most important diagnostic tool for the assessment of allergic contact dermatitis. Objective: This study documents the North American Contact Dermatitis Group (NACDG) patch testing results from January 1, 2013, to December 31, 2014. Methods: At 13 centers in North America, patients were tested in a standardized manner with a screening series of 70 allergens. Data were manually verified and entered into a central database. Descriptive frequencies were calculated, and trends were analyzed using χ2 test. Results: A total of 4871 patients were tested. There were 3255 patients (66.8%) who had at least 1 positive reaction and 2412 patients (49.5%) who were ultimately determined to have a primary diagnosis of allergic contact dermatitis. A total of 434 patients (8.9%) had occupationally related skin disease. There were 9726 positive allergic reactions. Compared with the previous reporting periods (2011-2012 and 2001-2012, including at least three 2-year cycles), positive reaction rates for the top 25 screening allergens statistically increased for 2 allergens: methylchloroisothiazolinone/methylisothiazolinone (6.4%; risk ratios, 1.26 [1.07-1.50] and 2.08 [1.84-2.37]) and hydroxyethyl methacrylate (2.6%; risk ratios, 1.34 [1.02-1.76] and 1.23 [1.00-1.51]). Methylisothiazolinone, which was added to the screening series for this 2013-2014 cycle, had the third highest positive reaction rate of allergens tested (10.9%). Four other newly added allergen preparations - formaldehyde 2% (7%), diphenylguanidine (3.8%), propylene glycol 100% (2.8%), and benzophenone-4 (2.1%) - all had reaction rates greater than 2%. Twenty-one percent of tested patients had at least 1 relevant allergic reaction to an allergen not on the NACDG series; 14.6% of these were occupationally related. The T.R.U.E. TEST (SmartPractice Denmark, Hillerød, Denmark) would have hypothetically missed one quarter to one third of reactions detected by the NACDG screening series. Conclusions: These results confirm that the epidemic of sensitivity to methylisothiazolinone previously documented in Europe is also occurring in North America. Patch testing with allergens beyond a standard screening tray is necessary for the complete evaluation of occupational and nonoccupational allergic contact dermatitis.
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