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Measles - Rubeola

Measles is a highly communicable respiratory disease characterized by symptoms such as fever, malaise, cough, conjunctivitis, coryza, Koplik spots, and a maculopapular rash that radiates downward from the head. Although measles is currently classified as eliminated within the United States, there are certain contexts (eg, outbreaks, international travel, etc.) in which transmission remains possible.

When measles is suspected, serology and molecular detection are used for diagnosis. Serology is also useful to assess immunity.

Quick Answers for Clinicians

Is laboratory testing required to confirm measles?

According to the CDC’s case definition for measles, a positive laboratory result in either an existing or epidemiologically linked case is required to confirm a measles diagnosis. For specific details, refer to the CDC’s case definition for measles.

How does recent or previous vaccination affect testing for measles?

Although unlikely, it is still possible for measles-vaccinated individuals to develop infection. Measles infection in vaccinated individuals is typically milder, and immunoglobulin M (IgM) antibodies may be low or undetectable. In those who are vaccinated, suspected measles infection can be confirmed by molecular detection or paired IgG serology (eg, of an acute and convalescent sample) that demonstrates increased antibodies over time.

How does measles elimination affect the reliability of serology?

In regions where measles has been declared eliminated or is nearly eliminated, false-positive serology increases in frequency due to cross-reactivity with other more common infections that have similar symptoms (eg, rubella, parvovirus, or human herpesvirus 6). The CDC currently recommends the use of molecular detection, in addition to IgM serology, to improve diagnostic accuracy.

Indications for Testing

Laboratory testing for measles is indicated in individuals who:

Present with symptoms consistent with infection (eg, febrile illness culminating in a maculopapular rash), especially after international travel or exposure to measles or a measles-like illness
Require presumptive evidence of immunity

Laboratory Testing

Diagnosis

Measles is primarily diagnosed using immunoglobulin M (IgM) serology and molecular detection (eg, by reverse transcription polymerase chain reaction [RT-PCR]).

False-positive serologic results are more likely in regions where measles has been eliminated, due to cross-reactivity with other more common viruses (eg, rubella, parvovirus, or human herpesvirus 6). Molecular detection (available through many state-run laboratories and the CDC) is useful to support diagnostic accuracy, such as when the timing of specimen collection (eg, within 0-2 days of rash onset) might impact serology.

Specimen Collection

The CDC recommends collecting serum and respiratory specimens (eg, throat swab, nasopharyngeal swab/aspirates) during the first visit with any patient who has symptoms consistent with measles. When possible, a urine sample should also be collected. Refer to the WHO Manual for the Laboratory-Based Surveillance of Measles, Rubella, and Congenital Rubella Syndrome for recommendations on specimen collection timing.

Confirmation of Immunity

When vaccination status is unknown or evidence of immunity is required, IgG serology can be used to assess immunity. The CDC recommends measles vaccination for any individual with negative or equivocal test results.