An attenuated live virus vaccine is available that induces lower levels of measurable antibody than that from natural infection. The test for IgG antibodies is best utilized to determine a patient's immune status to mumps. Seroconversion between acute and convalescent sera is considered strong evidence of current or recent infection. The best evidence for infection is a significant change on two appropriately timed specimens, where both tests are done in the same laboratory at the same time. Appearance of an IgM antibody response normally occurs 7-14 days after the onset of disease.
Testing immediately post-exposure is of no value without a later convalescent specimen.
While the presence of IgM antibodies suggests current or recent infection, low levels of IgM antibodies may occasionally persist for more than 12 months post-infection or immunization. Such a residual IgM response may be distinguished from early IgM response to infection by testing sera from patients 2-3 weeks later for changing levels of specific IgM antibodies. Assays for IgM are more useful than IgG assays, since cross-reactions have not been observed. Positive IgM mumps antibody suggests infection within the past 2-3 months. No significant level of detectable mumps virus antibody.