Measles, Mumps, and Rubella - Centers for Disease Control and ...

Vol. 47 / No. RR-8 MMWR 39• is not epidemiologically linked to a confirmed case, and• has not been serologically or virologically tested or has noncontributory serologicor virologic results.A confirmed case of measles• meets the laboratory criteria for measles or• meets the clinical case definition and is epidemiologically linked to a confirmedcase.Confirmed measles cases are routinely reported to CDC by state health departments.Laboratory DiagnosisThe laboratory criteria for measles diagnosis are:• a positive serologic test for measles IgM antibody, or• a significant rise in measles antibody level by any standard serologic assay, or• isolation of measles virus from a clinical specimen.A laboratory-confirmed case need not meet the clinical case definition. Serologicconfirmation should be attempted for every suspected case of measles and is particularlyimportant for any case that cannot be epidemiologically linked through a chain oftransmission to a confirmed case. However, reporting of suspected or probable cases,investigation of cases, and the implementation of control activities should not be delayedpending laboratory results.Blood for serologic testing should be collected during the first clinical encounterwith a person who has suspected or probable measles. The serum should be testedfor measles IgM antibody as soon as possible using an assay that is both sensitive andspecific (e.g., direct-capture IgM EIA method). Correct interpretation of serologic datadepends on the timing of specimen collection in relation to rash onset and on thecharacteristics of the antibody assay used. This timing is especially important for interpretingnegative results because IgM antibody may not be detectable with someless sensitive assays until at least 72 hours after rash onset. Measles IgM may be detectableat the time of rash onset, peaks approximately 10 days after rash onset, andis usually undetectable 30–60 days after rash onset. In general, if measles IgM is notdetected in a serum specimen obtained in the first 72 hours after rash onset from aperson whose illness meets the clinical case definition for measles, another specimenshould be obtained at least 72 hours after rash onset and tested for measles IgM antibody.Measles IgM is detectable for at least 1 month after rash onset. Persons withfebrile rash illnesses who are seronegative for measles should be tested for rubella.As measles becomes rare in the United States, the likelihood of obtaining falsepositive serologic results from measles IgM antibody testing increases. False positiveresults have been obtained by using a commercially available ELISA assay for measlesIgM in persons with parvovirus infection (fifth disease) (224 ). Confirmatorytesting by using an assay that is both sensitive and specific (e.g., direct-capture IgMEIA method) should be considered when IgM is detected in a patient with suspected