Contact sensitization to cobalt--multifactorial analysis of risk factors based on long-term data of the Information Network of Departments of Dermatology.

BACKGROUND: Cobalt contact sensitization in consecutively tested patients is common. The sources of exposure, and thus clinical relevance, are mostly unclear. OBJECTIVE: To examine (i) long-term time trends of sensitization, (ii) risk factors that may point to relevant exposures, and (iii) coupling with nickel sensitization. METHODS: Data of all patients patch tested with cobalt(II) chloride hexahydrate (1% pet.) between 1992 and 2012 (n = 185 050) in the Information Network of Departments of Dermatology (IVDK, www.ivkd.org) were subjected to descriptive stratified and Poisson regression analysis. RESULTS: The overall prevalence of positive patch test reactions was 5.23% (95% confidence interal 5.13-5.33%). Regarding time trends, there were significant increases for males aged 18-44 years and for females aged ≥45 years, and a significant variation of co-reactivity with nickel over time. Female sex almost doubled the risk of sensitization; age ≥45 years was associated with a 30% decrease in the risk of positive patch test reactions to cobalt, and atopic eczema with an approximately 20% increase. CONCLUSIONS: Notwithstanding some diagnostic difficulties with the test preparation, a persistent, notable proportion of cobalt sensitization, isolated or coupled with nickel allergy, can be observed. This warrants further in-depth research into causative exposures, both at the workplace and in consumers.