Rapid molecular diagnosis of measles virus infection in an epidemic setting

During the 2011 measles outbreak in Paris (France), patients with clinical suspicion of measles were tested for virological confirmation of measles virus (MV) infection. To assess the practical value of molecular diagnosis in an epidemic setting, 171 oral fluid samples and 235 serum samples collected from 270 patients were tested prospectively for MV-RNA using a novel one-step real-time RT-PCR assay including an internal control. Serum samples were also tested for MV-specific IgG and IgM antibodies. MV infection was confirmed by detection of MV-RNA and/or MV-IgM for 229 of the 270 patients. The results for the 102 cases with both serum and oral fluid samples available were used to compare the techniques. The detection rate of MV-RNA by RT-PCR was 98% (100/102) for oral fluid and 95% (97/102) for serum samples. The detection rate of MV-IgM was 85% (87/102). Negative MV-IgM results were observed mostly for serum samples collected early after the onset of the rash. A MV-RNA standard of known concentration obtained by in vitro transcription was used to quantify MV-RNA in samples. MV-RNA copy numbers were significantly higher in oral fluid than in serum samples, but did not correlate with time of sampling (within 1 week after the onset of the rash), patient age, or vaccination status. During the early stage of infection, the MV-RNA viral load in serum was lower in patients positive than in those negative for MV-IgG. In conclusion, the one-step real-time RT-PCR assay is a simple and sensitive tool suitable for MV diagnosis within hours.