Speed up public health decisions on scabies by skipping full-body exams

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In public health settings, limiting examination for scabies to the exposed components of both limbs had high sensitivity compared to full body examination, found a London School of Hygiene & Tropical Medicine data analysis.

For years, the diagnosis of scabies has relied on time-consuming and intrusive full-body examinations. Now, researchers have found that an exam of just a patient’s hands, feet and lower legs may have the potential to catch more than 90% of all scabies cases, regardless of severity. These speedier exams may be useful in public health assessments on the prevalence of scabies.

Scabies, a skin condition caused by the microscopic mite Sarcoptes scabiei, is a major public health problem in low- and middle-income tropical settings. There is no laboratory test for infestation and diagnosis is almost always made with clinical examination.

Scabies control relies traditionally on diagnosing individual patients, however there is increasing use of mass drug administration programmes. For mass drug administration to be a viables approach surveys of communities to gauge scabies prevalence will be needed.

In the new work, Michael Marks of the London School of Hygiene & Tropical Medicine and colleagues analysed data from three recent large population-based surveys of scabies in the Solomon Islands and Fiji. In all three surveys, examinations of covered the arms, legs, face and torso. If patients reported itching in the groin, buttocks or breasts, these areas were also examined. Exams in children under 1 year covered the whole body.

Reports of scabies in examined patients included which of nine body regions lesions were found in.

Based on the information where lesions were found, the team concluded that exams of exposed body regions – the hands, feet and lower legs – had close to 90% sensitivity for detecting scabies compared to a whole-body exam. Further restricting exams limited sensitivity, however, with a sensitivity of only 51.2% for exams of the hands alone.

“Our study adds valuable data to the development of a simplified diagnostic process for scabies that may be applied to guide decisions about future public health interventions,” the authors say.

Introduction: In most settings, the diagnosis of scabies is reliant on time-consuming and potentially intrusive clinical examination of all accesible regions of skin. With the recent recognition of scabies as a neglected tropical disease by the World Health Organization there is a need for standardised approaches to disease mapping to define populations likely to benefit from intervention, and to measure the impact of interventions. Development and validation of simplified approaches to diagnose scabies would facilitate these efforts.
Methods: We utilised data from three population-based surveys of scabies. We classified each individual as having scabies absent or present overall, based on whole body assessment, and in each of 9 regions of the body. We calculated the sensitivity of diagnosing the presence of scabies based on each individual body region compared to the reference standard based on whole body examination and identified combinations of regions which provided greater than 90% sensitivity. We assessed the sensitivity according to gender, age group, severity of scabies and the presence or absence of impetigo.
Results: We included 1,373 individuals with scabies. The body regions with highest yield were the hands (sensitivity compared to whole body examination 51.2%), feet (49.7%), and lower legs (48.3%). Examination of the exposed components of both limbs provided a sensitivity of 93.2% (95% CI 91.2–94.4%). The sensitivity of this more limited examination was greater than 90% regardless of scabies severity or the presence or absence of secondary impetigo.
Discussion: We found that examination limited to hands, feet and lower legs was close to 90% for detecting scabies compared to a full body examination. A simplified and less intrusive diagnostic process for scabies will allow expansion of mapping and improved decision-making about public health interventions. Further studies in other settings are needed to prospectively validate this simplified approach.
Author summary: Scabies, caused by infestation with the microscopic mite Sarcoptes scabiei, is a major public health problem worldwide, particularly in low- and middle-income tropical settings. The diagnosis of scabies is reliant on detection of characteristic signs on clinical examination. Examination of the whole body is time-consuming and intrusive, whereas a more limited examination might be sufficient to guide public health decisions. We analysed data from several large scabies prevalence surveys to see if a more limited examination of the body provided acceptable sensitivity. We found that limiting examination to the exposed components of both limbs had high sensitivity compared to full body examination. Further studies are needed to prospectively validate simplified diagnostic approaches and aid scale up of scabies control programmes.

Michael Marks, Daniel Engelman, Lucia Romani, Daniel Mason, Oliver Sokana, Mike Kama, Margot Whitfeld, Andrew C Steer, John Kaldor

PLOS material
PLOS Neglected Tropical Diseases abstract

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