Risk factors for scabies treatment resistance: a retrospective cohort study

BACKGROUND In order to successfully treat scabies and to prevent its spread, it is important to identify the factors that can influence the outcome of scabies treatment. OBJECTIVES This study was designed to evaluate the risk factors associated with treatment resistance scabies during use of an effective topical medication. METHODS A retrospective cohort study was performed in patients with scabies infestations confirmed by potassium hydroxide (KOH) examinations. Patient characteristics, clinical features and treatment history were collected. The treatment resistance group included patients with persistent scabies infestations for more than 28 days after initiation of antiscabies treatment with 5% permethrin cream. RESULTS In total, 138 patients with scabies infestations treated between January 2017 and December 2020 were included in this study. Of these, 100 (72.5%) patients were treated successfully, while 38 (27.5%) patients experienced treatment resistance. In the univariable analysis, risk factors for treatment resistance scabies included impaired cognitive function (OR = 2.66, 95% CI, 1.15-6.14), limited mobility (OR = 2.97, 95% CI, 1.30-6.83), inpatient status (vs. outpatient, OR = 3.3, 95% CI, 1.28-8.54), topical steroid use before diagnosis (OR = 3.52, 95% CI, 1.61-7.81), systemic steroid use before diagnosis (OR = 3.57, 95% CI, 1.26-10.34) and a positive KOH exam after the first treatment (OR = 7.25, 95% CI, 3.24-17.11). In the multivariable analysis, limited mobility (OR = 3.46, 95% CI, 1.02-12.11) and topical steroid use before diagnosis (OR = 3.65, 95% CI, 1.41-9.75) were significant predictive factors for treatment resistance scabies. CONCLUSIONS Scabies patients with limited mobility and topical steroid use before diagnosis are at high risk of treatment resistance. Dermatologists should take these findings into consideration when treating patients with scabies infestations.