The 2020 International Alliance for the Control of Scabies Consensus Criteria for the Diagnosis of Scabies

D. Engelman; J. Yoshizumi; R.J. Hay; M. Osti; G. Micali; S. Norton; S. Walton; F. Boralevi; C. Bernigaud; A.C. Bowen; A.Y. Chang; O. Chosidow; G. Estrada-Chavez; H. Feldmeier; N. Ishii; F. Lacarrubba; A. Mahé; T. Maurer; M.M.A. Mahdi; M.E. Murdoch; D. Pariser; P.A. Nair; W. Rehmus; L. Romani; D. Tilakaratne; M. Tuicakau; S.L. Walker; K.A. Wanat; M.J. Whitfeld; R.R. Yotsu; A.C. Steer; L.C. Fuller

Disclosures

The British Journal of Dermatology. 2020;183(5):808-820. 

In This Article

Abstract and Introduction

Abstract

Background: Scabies is a common parasitic skin condition that causes considerable morbidity globally. Clinical and epidemiological research for scabies has been limited by a lack of standardization of diagnostic methods.

Objectives: To develop consensus criteria for the diagnosis of common scabies that could be implemented in a variety of settings.

Methods: Consensus diagnostic criteria were developed through a Delphi study with international experts. Detailed recommendations were collected from the expert panel to define the criteria features and guide their implementation. These comments were then combined with a comprehensive review of the available literature and the opinion of an expanded group of international experts to develop detailed, evidence-based definitions and diagnostic methods.

Results: The 2020 International Alliance for the Control of Scabies (IACS) Consensus Criteria for the Diagnosis of Scabies include three levels of diagnostic certainty and eight subcategories. Confirmed scabies (level A) requires direct visualization of the mite or its products. Clinical scabies (level B) and suspected scabies (level C) rely on clinical assessment of signs and symptoms. Evidence-based, consensus methods for microscopy, visualization and clinical symptoms and signs were developed, along with a media library.

Conclusions: The 2020 IACS Criteria represent a pragmatic yet robust set of diagnostic features and methods. The criteria may be implemented in a range of research, public health and clinical settings by selecting the appropriate diagnostic levels and subcategories. These criteria may provide greater consistency and standardization for scabies diagnosis. Validation studies, development of training materials and development of survey methods are now required.

Introduction

Scabies is a contagious skin disease caused by Sarcoptes scabiei var. hominis, a human-specific ectoparasite of approximately 0·4 mm in size that is invisible to the naked eye.[1,2] Scabies is estimated to affect around 150–200 million people globally[3] with an estimated 455 million annual incident cases,[4] although the accuracy of these estimates is limited by a paucity of epidemiological data.[5] Scabies infestation exists in all countries, but with a higher burden in low-income settings and tropical areas, and among infants, children and adolescents.[6] Outbreaks are common in institutions and enclosed communities in both high-income and low-income settings, particularly where crowding occurs. Outbreaks impose considerable health and economic burden, and are often difficult to control.[7,8]

Scabies causes a rash, which may cause stigma, as well as itch that can lead to sleep disruption, difficulty with concentration and absenteeism from education and employment. Scabies predisposes to superficial bacterial skin infection (due mainly to Staphylococcus aureus and Streptococcus pyogenes),[9] which in turn can lead to serious complications including severe skin and soft-tissue infections, sepsis, glomerulonephritis and likely acute rheumatic fever.[10,11] Although the immune response is incompletely understood, infestation does not confer complete immunity and protection on further exposure.[12] Therefore, recurrent episodes, especially in children, are common in areas of high transmission.[13,14]

The course of a scabies infestation begins when a fertilized female mite burrows into the skin of an uninfected individual. Following primary infestation, individuals are usually asymptomatic for the incubation period of 4–6 weeks. Symptoms develop much more rapidly (hours to days) with subsequent infestations.[15] Itch and skin lesions, most commonly small scattered papules, often with excoriation, develop as a result of hypersensitivity to mites and their products.[1] Burrows may be found in some, but not all, cases. This pattern of symptoms and signs is known as 'common scabies' (also described as classical, typical, ordinary, standard, usual or normal scabies). In the most obvious cases, scabies may be readily recognized based on clinical presentation.[16,17] However, scabies can manifest with a wide spectrum of clinical signs and variable severities, making clinical diagnosis challenging.

Current approaches to the diagnosis of common scabies, including clinical assessment and laboratory tests, have been assessed in two systematic reviews.[18,19] These reviews identified the inconsistent and varied approaches to diagnosis, and the absence of a gold standard. Scabies can be confirmed by microscopy of skin scrapings; however, this method has low sensitivity[20,21] and requires specialized equipment, operator training and time, making it unsuitable for use in the low-income settings where the highest scabies burden persists.[22]

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