Enhanced detection of measles virus infection following successful development of a real-time reverse transcriptase PCR in respiratory and urine samples using the cepheid SmartCycler®

Abstract

Aims Despite WHO-reported elimination of measles in Australia, importation of cases remains frequent. Laboratory confirmation supplements clinico-epidemiological evidence of measles virus infection, and is needed to establish elimination. Nucleic acid testing (NAT) using the SmartCycler® platform for the detection of measles virus from combined nose and throat swabs (NTS), nasopharyngeal aspirates (NPA) and urine samples was developed. Methods One hundred samples collected from patients with suspected measles were tested in parallel using immunofluorescence antigen (IFA) and NAT with SmartCycler® and LightCycler® RT-PCR platforms. Where available, the performance of measles virus-specific IgM and IgG serology was also assessed. Results Using LightCycler® RT-PCR as the reference standard, measles virus was detected in 35 clinical samples. There was 100% concordance between the results of the SmartCycler® and the LightCycler®-based RT-PCR. The sensitivity and specificity of IFA compared to NAT was 34.3% and 96.5%, respectively. Testing urine in addition to NTS or NPA did not improve diagnostic yield. Measles-specific IgM was detected in 15/21 (71.4%) patients with specimens that were measles NAT positive. Discussion The performance of the SmartCycler® is comparable to the LightCycler® in the detection of measles virus. However, IFA had poor sensitivity and should not be used to confirm measles virus infection where NAT is available.