Objectives: To evaluate the effectiveness of mass treatment with ivermectin of scabies outbreak in institutional settings. To determine the factors, such as host susceptibility and scabetic exposure level associated with the onset of scabies.
Methods: The authors investigated a nosocomial scabies outbreak in a close psychiatric ward. The index case was a man with steroid-induced localized crusted scabies. Twenty-six patients were diagnosed with scabies, 4 of them had relapse of scabies, while no staff was infested. Despite frequent surveillance and treatment of symptomatic patients with 1% gamma-benzenehexachloride (γ-BHC: Lindane), new cases were observed. Thus, all 69 patients in the ward were treated with ivermectin (200μg/kg) simultaneously on day 105 of the outbreak (the mass treatment). Patients who had scabies were compared with patients who had no scabies in terms of age, body weight, diabetes, physical functions, topical administration of corticosteroid, proximity to the index patient, and problematic behavior.
Results: The mass treatment was implemented without a significant adverse event. Although two patients developed symptoms of scabies after the mass treatment, no patient in the ward had been diagnosed with scabies since the 98th day of the treatment. Regarding factors associated with the scabies onset, the only statistically significant factor was proximity to the index patient with crusted scabies.
Conclusions: Oral ivermectin was safe and effective for controlling scabies in institutional settings. The exposure level to scabetic mites was more important than host susceptibility in determining the risk of scabies onset.