The efficacy of sampling strategies for estimating scabies prevalence

BackgroundEstimating community level scabies prevalence is crucial for targeting interventions to areas of greatest need. The World Health Organisation recommends sampling at the unit of households or schools, but there is presently no standardised approach to scabies prevalence assessment. Consequently, a wide range of sampling sizes and methods have been used. As both prevalence and drivers of transmission vary across populations, there is a need to understand how sampling strategies for estimating scabies prevalence interact with local epidemiology to affect the accuracy of prevalence estimates.MethodsWe used a simulation-based approach to compare the efficacy of different scabies sampling strategies. First, we generated synthetic populations broadly representative of remote Australian Indigenous communities and assigned a scabies status to individuals to achieve a specified prevalence using different assumptions about scabies epidemiology. Second, we calculated an observed prevalence for different sampling methods and sizes.ResultsThe distribution of prevalence in subpopulation groups can vary substantially when the underlying scabies assignment method changes. Across all of the scabies assignment methods combined, the simple random sampling method produces the narrowest 95% confidence interval for all sample sizes. The household sampling method introduces higher variance compared to simple random sampling when the assignment of scabies includes a household-specific component. The school sampling method overestimates community prevalence when the assignment of scabies includes an age-specific component.DiscussionOur results indicate that there are interactions between transmission assumptions and surveillance strategies, emphasizing the need for understanding scabies transmission dynamics. We suggest using the simple random sampling method for estimating scabies prevalence. Our approach can be adapted to various populations and diseases.     

Reconstruction of proximal nasal defects with island composite nasal flaps

There are few local nasal flap options for repair of proximal nasal defects. Absence of suitable donor sites and the large dimensions of the defects limit the use of local nasal flaps in this region. Regional paranasal flaps may not be suitable in these cases because of color, texture, and donor-site scars. The composite procerus muscle and nasal skin flap, which is vascularized by the dorsal nasal branch of the angular artery, can be a useful treatment modality for proximal nasal reconstruction. Seven patients were successfully treated using the composite nasal flaps. The maximal size of the defects was 2.4 cm. In one case, the composite nasal flap was readvanced to close a new defect resulting from reexcision. The composite nasal flap has several advantages in reconstruction of proximal nasal defects. Reconstruction is performed with the same tissue and the donor defect is closed primarily. The composite nasal flap can be moved in multiple directions and has great mobility to reach every point of the proximal part of the nose with axial blood supply. Furthermore, it can be easily readvanced without additional morbidity in case of reexcision.