Vaccines and Preventable Diseases:
Mumps - Laboratory Testing for Mumps Infection Q&A
Clinical Questions and Answers
What specimens should be collected from patients meeting the clinical case definition?
CDC recommends that a blood specimen and buccal/oral swab be collected from all patients with clinical features compatible with mumps.
When is the best time to collect clinical specimens?
Among unvaccinated persons, if an acute IgM is collected 3 or less days after onset of parotitis and the IgM is negative, a second serum sample (collected 5-7 days after onset) is recommended. Buccal/oral swabs should also be collected at first contact.
Comment: unvaccinated persons include those with unknown vaccination history, and those with or without a history of mumps disease- older persons or foreign nationals may have detectable mumps IgG due to a previous subclinical infection.
Persons with a history of documented mumps vaccination, regardless of timing of collection, may not have detectable IgM. Buccal samples have the best chance of containing virus when collected on day 1-3 of onset of parotitis.
Why should I ask for viral samples such as buccal swabs in addition to the serum sample?
Buccal swabs samples can be tested for the presence of mumps virus (growth in culture) or mumps viral RNA using standard reverse transcriptase - polymerase chain-reaction (RT-PCR) methods.
What is the gold standard for laboratory confirmation of mumps?
Virus culture. Laboratories are strongly encouraged to perform cell culture isolation of mumps from buccal/oral swabs specimens. Primary monkey kidney cells and Vero cells have been used successfully. Detection of mumps in culture can be done using immunofluorescent antibody staining or standard RT-PCR.
What serological tests are used at CDC to diagnose mumps?
To detect mumps IgM, a capture EIA (non-quantitative) that uses recombinant mumps nucleocapsid (N) protein as antigen is used. A commercial, indirect EIA (non-quantitative) is used for detection of IgG.
What serological tests are available for use in the Public Health Laboratories?
There are commercially available immunofluorescence antibody assays for detection of mumps IgM and some EIA kits may be obtained. Since these assays are not FDA-approved for laboratory diagnosis of mumps cases, each laboratory must validate these tests independently.
If the suspected case has a positive IgG and negative IgM result, can mumps infection be ruled out?
In an outbreak setting, no. Previously vaccinated persons who are exposed to mumps will generally have existing, detectable serum IgG.
What is the protective neutralization titer for mumps?
There is no known protective neutralization titer or any other immune parameter(s) that correlates with protection from mumps disease. Immunized persons who are exposed will normally experience a boost in IgG titer.
Will persons infected with mumps who are symptomatic and have a history of one or two doses of MMR have an IgM response?
The IgM response to mumps infection in vaccinated persons is highly variable and may be absent. In unvaccinated cases, IgM is present by day 5 post onset of symptoms and peaks at about 1 week; IgM can be present for at least 6 weeks.
Is it possible to demonstrate a 4-fold rise in titer between paired serum samples (acute and convalescent) among cases of mumps with a history of 1 or 2 doses of MMR?
It may not be possible. In vaccinated persons, the existing IgG will begin to rise soon after exposure and infection. At the time of onset of symptoms and collection of the acute serum, the IgG may already be quite elevated, and obviate the 4-fold rise observed in convalescent serum specimen.
What etiologic agents are likely to interfere with serological assays (produce false positive) for mumps?
Parainfluenza viruses 1 and 3.
What does a positive result from RT-PCR mumps test from clinical material mean?
A positive RT-PCR signal indicates the presence of mumps viral RNA. The positive result should be used only to support a clinical diagnosis of mumps since persons recently immunized against mumps may have limited viral shedding following vaccination.
Why attempt to isolate mumps virus in cell culture?
Virus isolation is considered the best method to detect infection. Virus can be detected when IgM antibodies or IgG titer rise are not detected. Additionally, it provides virus that can be used for sequence studies. Finally, isolation studies are less likely than PCR assays to give false positive results because of contamination.
Why should PCR products from representative mumps cases and mumps viral isolates be submitted to CDC for sequence analysis?
The sequence of the PCR product will confirm positive PCR reactions. In addition, the sequence of the mumps short hydrophobic (SH) gene is used to assign mumps viruses to one of 12 recognized genotypes. The sequence information will help to identify the source of the virus, and can provide confirmation of suspected epidemiologic links.
Where can I find RT-PCR and real time RT-PCR protocols for mumps?
Protocols for both a standard RT-PCR and a real time RT-PCR targeting the short hydrophobic (SH) gene of mumps virus have been posted on the CDC web page (www.cdc.gov/vaccines/vpd-vac/mumps/outbreak/default.htm#lab).
Where do I obtain material for PCR and virus isolation controls?
CDC can provide a sample of RNA that has been purified from cells infected with mumps virus. This material is ready to use in RT-PCR assays with any set of primers. If laboratories would like to produce their own RNA samples or require a positive control for virus isolation, CDC can provide a sample of wild-type mumps virus. Public health laboratories or laboratories affiliated with state public health laboratories may send request for mumps RNA or virus to jrota@cdc.gov.
A sample tests negative for mumps RNA by RT-PCR or negative for mumps virus by isolation. Do these results rule out mumps infection?
No. These samples could be negative because the amount of virus shed at the time of sample collection was very low. Inadequate specimen collection, processing, shipping or storage can also significantly reduce the likelihood of detecting mumps virus or mumps RNA.
(www.cdc.gov/vaccines/vpd-vac/mumps/outbreak/default.htm#lab).
Among symptomatic persons who have received 1 or more doses of MMR, the virus may be cleared rapidly. The results to date do not indicate that RT-PCR for mumps among vaccinated persons has provided a diagnostic tool that is superior to IgM testing. However, samples collected when the patient first presents with symptoms have the best chance of having a positive result by RT-PCR.
References
- Gut JP. Lablache C. Behr S. Kirn A. Symptomatic mumps virus reinfections. Journal of Medical Virology. 45(1):17-23, 1995.
- Narita M. et al. Analysis of mumps vaccine failure by means of avidity testing for mumps virus-specific immunoglobulin G. Clinical & Diagnostic Laboratory Immunology. 5(6):799-803, 1998.
- Sartorius, B, et al. An outbreak of mumps in Sweden, February-April 2004. Eurosurveillance. 1:10 (9), 2005.
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Content last reviewed on March 18, 2008
Content Source: National Center for Immunization and Respiratory Diseases