What is the most appropriate testing for measles (Rubeola) diagnosis?

From the Guidelines

The most appropriate testing for measles is serologic testing for measles IgM antibody as soon as possible after the first clinical encounter, using an assay that is both sensitive and specific, such as the direct-capture IgM EIA method. This approach is supported by the Advisory Committee on Immunization Practices (ACIP) recommendations 1. When a patient presents with suspected measles, blood for serologic testing should be collected during the first clinical encounter. The serum should be tested for measles IgM antibody as soon as possible, and correct interpretation of serologic data depends on the timing of specimen collection in relation to rash onset and on the characteristics of the antibody assay used.

Key considerations for serologic testing include:

• Measles IgM may be detectable at the time of rash onset, peaks approximately 10 days after rash onset, and is usually undetectable 30-60 days after rash onset 1
• If measles IgM is not detected in a serum specimen obtained in the first 72 hours after rash onset from a person whose illness meets the clinical case definition for measles, another specimen should be obtained at least 72 hours after rash onset and tested for measles IgM antibody 1
• Measles IgM is detectable for at least 1 month after rash onset, and persons with febrile rash illnesses who are seronegative for measles should be tested for rubella 1

It is essential to note that prompt diagnosis is crucial for implementing isolation precautions and contact tracing to prevent further transmission, as measles is highly contagious. In real-life clinical practice, it is critical to prioritize testing methods that provide accurate and timely results, such as serologic testing for measles IgM antibody, to ensure effective disease management and prevention.

From the Research

Most Appropriate Testing for Measles

• The most appropriate testing for measles involves the detection of measles-specific IgM antibodies and viral nucleic acid 2.
• IgM detection shows highest sensitivity when serum samples are collected ≥5 days after rash onset 3.
• Virus isolation gives the highest sensitivity when samples are collected ≤3 days after rash onset, with nasopharyngeal aspirate being the best specimen type, followed by urine and throat/combined throat and nasal swab 3.
• RT-PCR positive rate of 100% was observed with throat/combined throat and nasal swab, urine, and nasopharyngeal aspirate collected ≤16,4-16, and 4-7 days after rash onset, respectively 3.

Comparison of Laboratory Diagnostic Methods

• The sensitivity of virus isolation using throat swabs and PBMC in comparison with RT-PCR was 58.1 and 93.5%, respectively 4.
• The percentage of positive results from PBMC by RT-PCR and virus isolation was 100 and 91.7%, respectively 4.
• The detection of measles virus RNA in PBMC by RT-PCR was the most effective method for diagnosis of measles 4.

Point-of-Care Testing

• A point-of-care test (POCT) for measles diagnosis showed a sensitivity and specificity of 90.8% and 93.6% with serum specimens, and 90.0% and 96.2% with oral fluids, respectively 2.
• Measles virus genes could be recovered from POCT strips after storage for 5 weeks at 20-25 °C 2.

Laboratory Diagnostic Methods

• Laboratory diagnostic methods for measles include indirect detection via antibody (IgM and IgG) detection methods and direct detection by viral culture or viral genome detection 5.
• Direct detection of viral genomic material using reverse transcription polymerase chain reaction (RT-PCR) methodologies can play an important role for laboratory confirmation of acute infections 5.
• Genotyping of measles virus provides useful molecular epidemiological data for differentiating vaccine from wild-type strains, linking cases and outbreaks, and tracking geographic spread and elimination 5.