Analysis of the reliability of rapid diagnostic tests for varicella, including breakthrough cases

In the era of universal varicella vaccination, diagnosis of varicella is challenging, especially for breakthrough cases. We sought to clarify the reliability of direct varicella-zoster virus (VZV) loop-mediated isothermal amplification (LAMP) and DermaQuick® VZV using the immunochromatography technique as rapid diagnostic tests for varicella. In addition, the usefulness of saliva as a sample type for direct LAMP was investigated. Among the 46 enrolled patients with suspected VZV infection, 31 patients (67.3%) were positive for the nucleic acid test based on real-time PCR from skin swab samples. Direct LAMP of skin swabs was positive in 29 (63.0%) of 46 patients. DermaQuick® VZV was positive in 25 (54.3%) of 46 patients. VZV DNA was detected in only 48.4% of oral swabs with the direct LAMP method. With real-time polymerase chain reaction (PCR) as the standard for diagnosing varicella, the sensitivity and specificity of DermaQuick® VZV were 80.7% and 100%, respectively. The sensitivity and specificity of direct LAMP from skin swabs were 93.6% and 100%, respectively. The sensitivity and specificity of real-time PCR for DNA extracted from oral swabs were 74.2% and 93.3%, respectively. Thus, oral swab samples are not suitable for breakthrough varicella diagnosis. Although DermaQuick® VZV is considered the most convenient point-of-care test for varicella, its sensitivity and specificity were lower than those of direct VZV LAMP.