Diagnostic Testing for Measles, Mumps, and Rubella
The recommended method for testing for measles, mumps, and rubella is serologic testing for virus-specific IgM antibodies using a sensitive and specific assay such as the direct-capture IgM EIA method, with blood collected during the first clinical encounter with a suspected case. 1, 2
Measles Testing Algorithm
- Collect blood for measles-specific IgM antibody testing at the first clinical encounter with a person who has suspected measles 1, 2
- Test serum using a direct-capture IgM EIA method, which is the most sensitive and specific assay 1, 3
- If the specimen is collected within the first 72 hours after rash onset and is negative, collect a second specimen at least 72 hours after rash onset 1, 3
- Measles IgM is typically detectable at rash onset, peaks approximately 10 days after rash onset, and remains detectable for 30-60 days 1, 3
- For additional confirmation, collect specimens for viral isolation (urine or nasopharyngeal mucus) as close to rash onset as possible 1, 3
- Molecular characterization of measles virus isolates through RT-PCR can provide valuable epidemiological information and distinguish between vaccine and wild-type strains 4, 3
Rubella Testing Algorithm
- Collect blood for rubella-specific IgM antibody testing as early as 1-2 days after rash onset 1
- Rubella IgM becomes detectable shortly after rash onset, peaks at approximately 7 days, and remains detectable for 4-12 weeks 1
- If IgM is not detectable in the first specimen, collect a second specimen 5 days after rash onset 1
- For congenital rubella syndrome, test cord blood for rubella-specific IgM antibodies 1
Mumps Testing Algorithm
- Collect blood for mumps-specific IgM antibody testing during the acute phase of illness 4
- Paired acute and convalescent serum specimens can demonstrate a significant rise in mumps antibody titer 4
- RT-PCR testing of buccal swab specimens provides direct detection of mumps viral RNA 4, 5
Important Clinical Considerations
- Laboratory confirmation should be attempted for every suspected case of measles, mumps, and rubella 1, 3
- Immediately notify local health departments of suspected cases; do not delay control activities pending laboratory results 1, 2
- False-positive IgM results may occur with certain conditions, such as parvovirus infection (fifth disease), requiring confirmatory testing 2, 3
- IgM testing should only be performed when acute illness is suspected; IgG testing alone is appropriate when evaluating for immunity 5
- Recent studies show that commercially available IgM detection methods for measles and rubella have high pooled sensitivity (94% and 97% respectively) and specificity (94% and 96% respectively) 6
Common Pitfalls and Caveats
- Using IgM testing inappropriately for immunity screening rather than acute infection diagnosis 5
- Collecting specimens too early (within first 72 hours of rash onset) may lead to false-negative results 2, 3
- Delaying collection of specimens for viral isolation reduces the chance of successful virus isolation 3
- Failing to collect a second specimen when the first IgM test is negative but clinical suspicion remains high 2, 1
- Not considering the possibility of false-positive IgM results in areas with low disease prevalence due to high vaccination rates 4, 6
Point-of-care tests for measles diagnosis are being developed with promising sensitivity and specificity for both serum (90.8% and 93.6%) and oral fluid specimens (90.0% and 96.2%), which may enhance field-based testing capabilities 7.