The efficacy of a nested polymerase chain reaction in detecting the cytochrome c oxidase subunit 1 gene of Sarcoptes scabiei var. hominis for diagnosing scabies

Summary Background A widespread scabies infestation, associated with long‐term residence in nursing homes, is becoming an issue in high‐income countries. Mineral oil examination is regarded as the gold standard in diagnosing scabies, but the sensitivity of this method is generally low – approximately 50%. Molecular techniques may contribute to enhancing the sensitivity of current tests for laboratory diagnosis of human scabies. Objectives To develop new primers for a nested polymerase chain reaction (PCR) for the cytochrome c oxidase subunit 1 (cox1) gene of Sarcoptes scabiei var. hominis to increase the sensitivity of a previously developed conventional PCR. Methods Patients with clinically suspected scabies underwent dermoscopy‐guided skin scraping with microscopic examination. The diagnosis was positive for scabies when mites or eggs were found under the microscope, and patients were then designated as ‘microscopy positive’. Patients who presented with negative microscopic results were placed in the ‘microscopy‐negative’ group. Skin scrapings were collected from both groups for PCR. Results Of the total 63 samples, 28 were microscopy positive and 35 were negative with no differences in sex and age between the two groups. All microscopically proven cases of scabies were positive using the cox1 nested PCR. Among microscopy‐negative samples, S. scabieiDNA was detected in nine. If sensitivity of the cox1 nested PCR is considered 100% [95% confidence interval (CI) 90·5–100], then sensitivity of microscopy is 75·7% (95% CI 58·8–88·2; P = 0·004). Conclusions Nested PCR can be successfully used as an alternative method for diagnosing suspected scabies. Therefore, infection control measures and treatments can be initiated before significant transmission occurs, minimizing the risk of outbreaks. What's already known about this topic? Previous studies have demonstrated the usefulness of conventional polymerase chain reaction (PCR) in diagnosing scabies but the positive diagnosis rate was too low to obtain satisfactory results. Research comparing PCR for scabies diagnosis against microscopy detection did not include dermoscopy; therefore, it is possible that there were high false‐negative rates by microscopy and the effectiveness of a PCR assay was overstated. What does this study add? The detection rate of scabies by nested PCR in patients who were microscopy negative (26%, nine of 35 samples) was higher than by conventional PCR (14%, 12 of 83 samples). Even thoug