Reevaluation of laboratory methods for diagnosis of measles

The purpose of this study is to reevaluate the sensitivities of different methods used in the diagnosis of measles including virus isolation, RT-PCR, and measurement of IgM. Sixty-three throat swabs, 84 peripheral blood mononuclear cell (PBMC) samples, and 85 plasma samples were collected from 85 cases of suspected measles. The sensitivity of virus isolation using throat swabs and PBMC in comparison with RT-PCR was 58.1 and 93.5%, respectively. We defined laboratory-confirmed cases as those in which at least one of the methods was positive. The percentage of positive results by the different methods was compared among 49 laboratory-confirmed cases. The percentage of positive results from PBMC by RT-PCR and virus isolation was 100 and 91.7%, respectively. The percentage of positive results from throat swabs by RT-PCR and virus isolation was 91.2 and 52.8%, respectively. The percentage of IgM positive (79.6%) was significantly lower than that of PBMC by RT-PCR. Ten of 27 plasma samples collected within 5 days of the onset of fever were IgM negative. In contrast, all of the 21 plasma samples collected 6 days after the onset of fever were IgM positive. In conclusion, the detection of measles virus RNA in PBMC by RT-PCR was the most effective method for diagnosis of measles.