Utility of neutralization test for laboratory diagnosis of suspected mumps.

Mumps is an infectious disease caused by mumps virus (MuV), which belongs to the family Paramyxoviridae and genus Rubulavirus. Typical symptoms of mumps include fever and swelling of the parotid glands; however, mumps can be asymptomatic. Mumps is diagnosed by molecular and serological methods (i.e., PCR and Enzyme Immunoassay [EIA]); however, both methods have pros and cons. This study was performed to compare the diagnostic utility of a focus reduction neutralization test (FRNT) to that of MuV-specific commercial IgM and IgG antibody EIA in patients suspected of having mumps. One hundred-eighty six samples collected during mumps outbreak in 2012-16 were studied. Samples (n = 80) were tested by all the three serological assays and showed 70.4%, 83% and 92.5% positivity by IgM EIA, IgG and FRNT, respectively. In all, 58.8% samples (n = 47) tested positive in all three assays. Concordance between mumps RT-PCR and IgM EIA was highest during the first 2-5 days and decreased with increasing time post-onset. Mumps FRNT results agreed with those of RT-PCR/IgM EIA from the second week onwards, whereas the results of mumps IgG EIA agreed with those of RT-PCR/IgM EIA from post-onset days 3-10. These findings suggest the utility of a FRNT for laboratory diagnosis of mumps in countries whose populations are not immunized against this infection.