Agreement between clinical criteria and quantitative polymerase chain reaction for diagnosing scabies in Auckland children

Aim

We sought to determine the degree of agreement between clinical and laboratory methods for diagnosing scabies in school-aged children.

Methods

Clinical information and samples were collected from children aged 7 months to 14 years attending educational institutions in Auckland, New Zealand. Two methods determined scabies status: the International Alliance for the Control of Scabies clinical criteria (IACS) and quantitative polymerase chain reaction (qPCR). Sensitivity and specificity of each method, as the reference or index standard, were estimated and agreement was determined using Cohen's kappa statistic.

Results

Sixteen of 145 children were positive based on IACS criteria and 15 of 64 with a suspicious skin lesion returned a positive qPCR test. IACS sensitivity and specificity were 66.7% (95% confidence interval (CI): 39.9–93.3) and 94% (95% CI: 89.9–98.0), respectively (with qPCR as the reference). For qPCR, sensitivity and specificity were 50% (95% CI: 25.5–74.5) and 96.9% (95% CI: 94.0–100.0), respectively (with IACS as the reference). The kappa value was 0.53.

Conclusion

Agreement between clinical and laboratory methods in the identification of scabies diagnosis was moderate. Both methods had low sensitivity but high specificity. Scabies diagnosis might be improved, thereby enhancing control measures, by relaxing the IACS criteria (as some IACS-negative participants returned positive qPCR tests, indicating mite DNA was present) and conversely supplementing clinical assessment with qPCR testing.