Risk factors for treatment failure in scabies: a cohort study

Background Treatment failure, which occurs in about one-third of cases, is considered as a major factor in the increasing incidence of scabies in developed countries. Objectives To identify predictors of treatment failure of scabies in ambulatory populations. Methods This multicentre study compared the clinical characteristics and treatment modalities between a group of patients with scabies treated successfully and another group who were not cured 3 months after antiscabies treatment. Results In total 210 patients with a diagnosis of scabies were included, comprising 98 patients in the treatment success group and 112 in the treatment failure group. The main risk factors for treatment failure were (i) the use of only one type of treatment, topical benzyl benzoate (BB) or oral ivermectin, vs. the combination of both treatments [odds ratio (OR) 2 center dot 15, 95% confidence interval (CI) 1 center dot 22-3 center dot 77]; (ii) the use of a single intake (vs. two) of oral ivermectin (OR 10 center dot 2. 95% CI 4 center dot 49-23 center dot 2); (iii) intake of ivermectin during a meal vs. on an empty stomach (OR 4 center dot 31, 95% CI 1 center dot 89-9 center dot 84); (iv) absence of decontamination of furnishings (OR 8 center dot 72, 95% CI 3 center dot 50-21 center dot 8), in particular sofa and cushions (OR 5 center dot 90, 95% CI 2 center dot 34-14 center dot 9), mattresses (OR 4 center dot 16, 95% CI 1 center dot 35-12 center dot 8) or car seats (OR 6 center dot 57, 95% CI 3 center dot 27-13 center dot 2) and (v) absence of written documents explaining treatment modalities (OR 5 center dot 18, 95% CI 2 center dot 57-10 center dot 4). In multivariate analysis, treatment failure was mainly associated with (i) use of a single intake (vs. two) of ivermectin (OR 6 center dot 62, 95% CI 2 center dot 71-16 center dot 2); (ii) use of BB alone vs. two intakes of ivermectin (OR 3 center dot 51, 95% CI 1 center dot 55-7 center dot 95) and (iii) absence of decontamination of furniture with acaricides (OR 5 center dot 81, 95% CI 1 center dot 96-16 center dot 7). Conclusions Use of topical BB alone and a single intake (vs. two) of ivermectin are predictors of treatment failure.