Consensus criteria for the diagnosis of scabies: A Delphi study of international experts

Background: Scabies was added to the WHO Neglected Tropical Diseases portfolio in 2017, and further understanding of the disease burden is now required. There are no uniformly accepted test methods or examination procedures for diagnosis, which limits the interpretation of research and epidemiological findings. The International Alliance for the Control of Scabies (IACS) designated harmonization of diagnostic procedures as a priority for the development of a global control strategy. Therefore, we aimed to develop consensus criteria for the diagnosis of scabies. Methodology / Principal findings: We conducted an iterative, consensus (Delphi) study involving international experts in the diagnosis of scabies. Panel members were recruited through expression of interest and targeted invitation of experts. The Delphi study consisted of four rounds of anonymous surveys. Rounds 1 and 2 involved generation and ranking an extensive list of possible features. In Rounds 3 and 4, participants were presented results from previous rounds and indicated agreement with a series of draft criteria. Panel participants (n = 34, range per Round 28–30) were predominantly highly experienced clinicians, representing a range of clinical expertise and all inhabited continents. Based on initial rounds, a draft set of criteria were developed, incorporating three levels of diagnostic certainty–Confirmed Scabies, Clinical Scabies and Suspected Scabies. Consensus was reached in Round 4, with a very high level of agreement (> 89%) for all levels of criteria and subcategories. Adoption of the criteria was supported by 96% of panel members. Conclusions / Significance: Consensus criteria for scabies diagnosis were established with very high agreement. The 2018 IACS Criteria for the Diagnosis of Scabies can be implemented for scabies research and mapping projects, and for surveillance after control interventions. Validation of the criteria is required. Author summary: Scabies causes rash and severe itch and predisposes to serious infection and chronic diseases of the heart and kidneys. Despite scabies being an ancient disease found in all parts of the world, we currently lack reliable laboratory tests. Clinicians generally make an assessment based on history and skin examination. Variation in diagnosis causes problems when trying to determine the prevalence of scabies in a region, or when trying to investigate the effectiveness of a treatment or control strategy. We aimed to establish consensus among experts on how to diagnose scabies. Thirty-four international experts responded to anonymous questionnaires on how tests and clinical features of scabies should be used to form a diagnosis. Draft criteria were developed and refined, incorporating three levels of diagnostic certainty–Confirmed Scabies, Clinical Scabies and Suspected Scabies. After three rounds of surveys, 82% of participants supported the criteria. After four rounds, consensus was reached with very high agreement for all criteria (Confirmed Scabies, 96%; Clinical Scabies, 93%; Suspected Scabies, 100%) and 96% supported adoption of the criteria. It is hoped the 2018 IACS Criteria for the Diagnosis of Scabies will allow harmonization of diagnosis and reporting, and comparison between studies of scabies burden and treatments.