title: Methylisothiazolinone testing at 2000 ppm: a prevalent sensitizer for allergic contact dermatitis.
abstract: BACKGROUND
  Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) have been identified as potent allergens. The optimal MI concentration for patch testing for reaction to these agents has not yet been identified, but it has been suggested that testing MI at 2000 ppm may reduce false-negative reactions.
  
  
  OBJECTIVE
  The aim of this study was to report allergic reactions to MI and MCI/MI detected in a community dermatology practice setting in Ontario, Canada.
  
  
  METHODS
  The patch test records of patients with suspected allergic contact dermatitis seen between October 2007 and June 2014 were reviewed. We compared positive patch testing before and after December 2011 when a higher MI concentration was used (2000 ppm aqueous) in addition to the baseline series MCI/MI at 100 ppm.
  
  
  RESULTS
  A total of 794 patient records were reviewed. There were 38 true-positive reactions to MI or MCI/MI. Of these 38 patients, 26 (68%) were female. We detected an overall increase in the rate of positive patch testing to MCI/MI, MI alone, or both from 3.13% to 7.45% when MI concentration was introduced at 2000 ppm aqueous. Occupational differences existed between sexes.
  
  
  CONCLUSIONS
  The addition of MI at 2000 ppm to our screening series effectively increased the detection of MI-induced allergic contact dermatitis.
authors.affiliation: From the Skin Centre for Dermatology, Peterborough, Ontario, Canada.
authors.forename: Kaiya
authors.initials: K
authors.lastname: Ham
authors.forename: Claudia J
authors.initials: CJ
authors.lastname: Posso-De Los Rios
authors.forename: Melinda
authors.initials: M
authors.lastname: Gooderham
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D017449:Dermatitis, Allergic Contact / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D004202:Disinfectants / Q000009:adverse effects*; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010328:Patch Tests / Q000379:methods*; D015995:Prevalence; D012189:Retrospective Studies; D013844:Thiazoles / Q000009:adverse effects*; D055815:Young Adult
chemical_list: D004202:Disinfectants; D013844:Thiazoles; C011506:2-methyl-4-isothiazolin-3-one; C011421:5-chloro-2-methyl-4-isothiazolin-3-one