Measurement of risk of sensitisation and its application to Kathon.

The prevalences of patch test reactions to 27 common allergens including Kathon 100 ppm, were calculated in a standard test battery applied to 2 consecutive cohorts of 656 and 653 patients seen in 1985/6 and 1986/7. The overall prevalence of Kathon sensitivity was 0.9% for 1985-87. The prevalence for 1985/6 and 1986/7 was 0.8% and 1.1% (difference not significant). The rate of sensitisation to Kathon was measured in 212 patients with negative patch tests by retesting after 6-15 months (mean 10.8 months +/- 0.2 SE), and gave a mean rate of sensitisation of 1/2280 patient months or 0.5%/patient population. Retesting 45 negative reactors after 4 weeks gave no new reactors, showing that the rate of sensitisation by patch testing with 100 ppm Kathon is low. It is concluded that the low and stable prevalence of Kathon sensitivity and the low rate of new sensitisation is in keeping with a low potential for sensitisation. Used on a larger scale, the present method would rapidly define risk from potential new allergens.