LABORATORY CONFIRMATION The CDC recommends determination of any one of the following to help confirm the diagnosis of acute mumps infection. • Presence of serum mumps IgM antibodies • Significant rise in IgG antibody titer between the acute and convalescent-phase serum specimens • IgG seroconversion • Positive mumps virus culture • Detection of virus by real-time reverse transcriptase polymerase chain reaction (RT-PCR)4
Antibody testing At the initial visit, a serum specimen should be obtained to test for mumps IgM antibodies.4 The CDC recommends enzyme immunoassay (EIA) testing for IgM antibodies to confirm acute mumps infection.4
IgM antibodies are detectable five days after onset of symptoms and, after reaching a maximum level, remain elevated for several weeks. If the initial IgM test is negative, the test can be repeated in five to seven days.4
Either EIA or immunofluorescence antibody assay (IFA) testing for mumps IgG antibodies should be performed on both acute- and convalescent-phase serum samples. Laboratory confirmation requires a fourfold rise in the antibody titer using a quantitative assay4 or seroconversion from negative to positive.
Virus detection If possible, mumps virus samples should be obtained no more than three to eight days after symptom onset because delay may result in a low viral yield.4 The best viral samples are obtained via parotid duct swabs (see Figure 2). Before swabbing the buccal cavity, the parotid gland should be massaged for 30 seconds to ensure that the specimen contains gland secretions.4
Mumps virus can be detected by RT-PCR or culture. The RT-PCR is currently the most sensitive test for mumps, but most RT-PCR testing is done by public health laboratories and the CDC, and results may not be available until after the illness has resolved.4
Laboratory tests, however, are not always helpful in confirming a clinical diagnosis of mumps. Vaccinated persons may not mount a secondary immune response to mumps and consequently may not have a significant IgM response. It is also possible that a high level of IgG antibodies will cause a false-positive IgM test results.4
Other laboratory tests that may support a diagnosis of mumps include a complete blood cell count, which may reveal a leukopenia with relative lymphocytosis or neutrophil leukocytosis,16 and a measurement of serum amylase level which, if elevated, may confirm the inflammatory process.10 See Table 1 for a summary of tests that confirm or support a mumps diagnosis.
Mumps is a reportable illness, and the local health department should be contacted for assistance with determining where and how to ship specimens.17 However, in the absence of laboratory confirmation, only clinical cases with parotitis, other salivary gland involvement, or mumps-related complications are notifiable.11
