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

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. What is already known about this topic? The diagnosis of scabies is limited by the lack of accurate, objective tests. Microscopy of skin scrapings can confirm the diagnosis, but it is insensitive, invasive and often impractical. Diagnosis usually relies on clinical assessment, although visualization using dermoscopy is becoming increasingly common. These diagnostic methods have not been standardized, hampering the interpretation of findings from clinical research and epidemiological surveys, and the development of scabies control strategies. What does this study add? International consensus diagnostic criteria for common scabies were developed through a Delphi study with global experts. The 2020 International Alliance for the Control of Scabies (IACS) Criteria categorize diagnosis at three levels of diagnostic certainty (confirmed, clinical and suspected scabies) and eight subcategories, and can be adapted to a range of research and public health settings. Detailed definitions and figures are included to aid training and implementation. The 2020 IACS Criteria may facilitate the standardization of scabies diagnosis.

Figure 1

Optical microscopy of skin scrapings for diagnosis of scabies. (a) Female scabies mite, magnification × 200. (b) Eggs of a scabies mite, magnification × 200. (c) Faecal pellets (scybala) are seen as small oval structures, magnification × 400.

Figure 2

Direct visualization of a scabies mite. (a) Scabies burrow on the finger web space (arrow), visible with the naked eye. The V‐shaped scale (‘wake sign’) is visible at the top (arrowhead). (b) Visualization of the scabies burrow from (a) using dry dermoscopy (magnification × 10). The open portion of the ‘V’ points to the intact entrance of the burrow. The female scabies mite is seen at the distal end of the burrow as a brown triangular spot (arrowhead). (c) Videodermoscopy image of a burrow (magnification × 200). The oval body of the female scabies mite (circle), its eggs (arrows) and its faecal pellets (arrowheads) are visible. (d) In vivo reflectance confocal microscopy image (field of view 0·75 × 0·75 mm) of the female mite. The oval body is visible within the epidermis (upper stratum granulosum), along with its head (arrowhead), anterior legs (arrows) and faecal pellets (asterisks).

Figure 3

Skin examination findings of scabies. (a) Papules over the fingers, finger web spaces and back of hand of an adult. (b) Papules and vesicles with excoriation on the volar wrist of a child. (c) Papules, vesicles and pustules with excoriations over the palm and fingers of an infant. (d) Widespread scabies rash in an infant. Larger nodules are seen on the torso, axilla and shoulder. (e) Papules over the toes, feet and ankle of an infant. (f) Ulcers, pustules and crust representing impetiginization (secondary bacterial infection) of scabies lesions on the legs of a child. (g) Papules and nodules on the scrotum and penis. Lesions are also seen on the groin and inner thighs. (h) Crusted scabies with thick, yellowish scale of the right hand.

Figure 4

Typical distribution of scabies lesions. (a) Children aged > 2 years and adults. (b) Infants aged < 2 years.