Comparison of laboratory diagnostic methods for measles infection and identification of measles virus genotypes in Hong Kong.

The sensitivities of IgM detection, virus isolation, and RT-PCR for the diagnosis of measles infection were assessed using samples collected from confirmed measles cases from 2006 to 2009. The optimal timing of specimen collection and the preferred specimen type(s) for these tests were also determined. IgM detection showed highest sensitivity when serum samples were collected >or=5 days after rash onset. Virus isolation gave the highest sensitivity when samples were collected <or=3 days after rash onset, with nasopharyngeal aspirate being the best specimen type, followed by urine and throat/combined throat and nasal swab. The highest RT-PCR positive rate (81.0%) was obtained with serum samples collected <or=3 days after rash onset. RT-PCR positive rate of 100% was observed with throat/combined throat and nasal swab, urine and nasopharyngeal aspirate collected <or=16, 4-16, and 4-7 days after rash onset, respectively. The genotype of each measles case was confirmed by sequencing. It was shown that the predominant measles viruses detected in Hong Kong during 2006-2009 belonged to genotype H1 (subtype a) and these strains were related closely to those detected in China.