From the Guidelines
The best way to diagnose measles is through a combination of clinical evaluation and laboratory testing, with a focus on serological tests for measles-specific IgM antibodies or detection of measles virus RNA by reverse transcription polymerase chain reaction (RT-PCR) from specimens collected from the throat, nasal passages, urine, or blood, as recommended by the most recent and highest quality study 1. The diagnosis of measles should start with a clinical evaluation, assessing for characteristic symptoms including high fever, cough, runny nose, red watery eyes, and the distinctive maculopapular rash that typically begins on the face and spreads downward to the rest of the body.
- Key symptoms to look out for include:
- High fever
- Cough
- Runny nose
- Red watery eyes
- Maculopapular rash Laboratory confirmation is essential and involves either a serological test for measles-specific IgM antibodies or detection of measles virus RNA by reverse transcription polymerase chain reaction (RT-PCR) from specimens collected from the throat, nasal passages, urine, or blood, as supported by 1.
- The most effective laboratory tests for diagnosing measles include:
- Serological tests for measles-specific IgM antibodies
- Detection of measles virus RNA by reverse transcription polymerase chain reaction (RT-PCR) Specimens should ideally be collected within 3 days of rash onset for viral detection, though IgM antibodies are usually detectable 3-4 days after rash appearance and remain positive for about 4 weeks, as noted in 1. Early diagnosis is crucial for implementing isolation measures to prevent transmission, as measles is highly contagious, and the virus can be detected before the characteristic rash appears, which is important for outbreak control, as highlighted in 1. Clinicians should maintain a high index of suspicion in unvaccinated individuals or in those with recent travel to endemic areas, and consider the use of airborne infection–control precautions and implementation of other infection-control measures to control the spread of measles, as recommended in 1.
From the Research
Diagnosis of Measles
The diagnosis of measles can be achieved through various methods, including:
- Clinical case definition: A generalized maculopapular rash, fever (>or=38.3 degrees C, if measured), and either a cough, coryza, or conjunctivitis 2
- Serological confirmation: Hemagglutination inhibition assay, complement fixation assay, or enzyme immunoassays 2
- Detection of immunoglobulin M (IgM) antibodies: A sensitive method for laboratory confirmation of measles virus infection, especially in developing countries 3
- Virus isolation: Can be performed using B95a cells, but has a lower positive rate compared to IgM antibody test 3
- Reverse transcriptase PCR (RT-PCR) analysis: Can be used in combination with IgM detection on filter paper blood samples for diagnostic and epidemiological studies of measles 4
Laboratory Confirmation
Laboratory confirmation of measles is essential, especially in settings of low incidence, as the positive predictive value of the clinical case definition decreases significantly 2. The use of IgM antibody test, RT-PCR analysis, and virus isolation can provide accurate diagnosis of measles. However, the interpretation of a positive IgM result can be complicated in persons with a recent history of measles vaccination 5.
Diagnostic Approaches
Different diagnostic approaches have been evaluated, including:
- Combination of RT-PCR and IgM detection on filter paper blood samples: Has a sensitivity and specificity of 99 and 96%, respectively 4
- IgM antibody test: A sensitive method for laboratory confirmation of measles virus infection, especially in developing countries 3
- Clinical case definition: Can be used for initial screening, but serological confirmation is essential for accurate diagnosis 2