Prevalence and Determinants of Sensitisation to Neomycinin North-Eastern Italy, 1997–2021

Background: Allergic contact dermatitis (ACD) induced by topical application of neomycin is frequently reported. Objectives: This multi-center study investigated prevalence and determinants of neomycin sensitisations in 30 629 outpatients from North-eastern Italy during 1997–2021. Patients and Methods: European baseline and extended Triveneto series were applied on the upper back of patients patch testing for suspected ACD and removed after 48h. Results: Prevalence of neomycin sensitisation was 2.29% (=701/30629), significantly decreasing over time, especially after 2003. Neomycin sensitisation increased with age, especially in female patients older than 60 with leg dermatitis. The majority of patients sensitised to neomycin (74.5%) tested positive also against other haptens, particularly ingredients included in creams and emollients, as lanolin or benzocaine or preservatives as thimerosal or parabens. Conclusions: The decreasing prevalence of neomycin sensitisation over time likely reflected reduced accessibility and circulation of neomycin in Italy, due to containment of prescriptions and over-the-counter accessibility. Older individuals are typically more likely to be treated by topical medications and antibiotics as neomycin for various conditions, including stasis dermatitis. Since ACD caused by topical medications is relatively easy to miss, comprehensive drug history and patch testing are essential for any patient with suspected sensitisation caused by neomycin.