Analysis of serum IgM antibody and viral nucleic acid test results in measles and rubella cases in China from 2014 to 2023

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Objective: To analyze the results of serum IgM antibody and viral nucleic acid testing in measles and rubella cases in China from 2014 to 2023. Methods: Surveillance data on measles and rubella during 2014-2023 were obtained from the Chinese Disease Prevention and Control Information System, and cases that underwent measles/rubella IgM antibody testing and viral nucleic acid testing were included in the study. Information on the number of cases, vaccination status, and laboratory test results was collected, and laboratory test results were compared among cases with different times of rash or onset and different doses of vaccination. Results: From 2014 to 2023, the total number of measles and rubella surveillance cases was 581 746, and the number of measles and rubella cases that underwent both IgM antibody and viral nucleic acid testing was 39 124 and 21 766, respectively, with a double-positive rate of IgM antibody and viral nucleic acid testing of 63.73% (for measles) and 41.68% (for rubella). The single-positive rate for IgM antibody was 21.12% (for measles) and 27.15% (for rubella). The single-positive rate for viral nucleic acid tests was 13.84% (for measles) and 28.19% (for rubella). According to different days of rash or onset (0-3, 4-5, 6-10 and >10), samples of 24 629 (62.95%) measles cases and 15 785 (72.52%) rubella cases were from within 3 days of rash or onset, and the single positive rate of viral nucleic acid detection was 16.90% (for measles) and 32.07% (for rubella). The single positive rate of IgM antibody increased gradually with the time of onset (measles: χ2trend=314.098, P<0.001, rubella: χ2trend=763.846, P<0.001), and reached 31.66% (for measles) and 53.12% (for rubella) after 10 days of rash or onset. Depending on the number of vaccination doses (1, 2,≥3), the single positive rate of viral nucleic acid detection ranged from 12.93% to 20.29% (for measles) and from 25.30% to 27.88% (for rubella). The single positive rate of IgM antibody detection ranged from 36.89% to 47.47% (for measles) and from 22.81 to 41.15% (for rubella). Conclusions: Combined testing of serum IgM antibody and viral nucleic acids could facilitate laboratory confirmation of measles and rubella cases and was also important for measles and rubella elimination efforts.