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Questions and Answers about Lab Testing

Questions and Answers

General Laboratory Testing

Q: What specimens should be collected from patients who meet the mumps clinical case definition?

A: CDC recommends that a buccal or oral swab specimen and a blood specimen be collected from all patients with clinical features compatible with mumps. See Specimen Collection, Storage, and Shipment for detailed instructions regarding recommended samples for mumps testing.

Q: When is the optimal timing for collection of specimens for laboratory confirmation of mumps?

A: The acute-phase serum and clinical samples for detection of virus should be collected as soon as possible upon suspicion of mumps disease. The early collection of buccal swab specimens provides the best means of laboratory confirmation, particularly among suspected mumps patients with a history of vaccination.

Q: What tests are available for laboratory confirmation of mumps?

A: Standard serologic assays that detect mumps IgM are commercially available in both EIA and IFA formats. Viral detection methods include standard methods of culturing virus in appropriate cell lines and techniques, such as real time RT-PCR to detect mumps viral RNA.

Q: Where do I send laboratory specimens for testing?

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Mumps Viral Testing

Q: Why should I ask for buccal or oral swab specimens in addition to the serum sample?

A: Buccal and oral swab samples enhance the ability to laboratory-confirm a mumps infection and can provide additional information (sequence analysis to obtain the mumps genotype) to aid epidemiologic investigations. Because serologic tests cannot differentiate between an exposure to vaccine and an exposure to wild-type mumps virus, it is necessary to obtain other clinical samples to determine the genotype (wild-type vs. vaccine).

Q: What does a mumps-negative RT-PCR result mean?

A: : Failure to detect mumps virus RNA by RT-PCR in samples from a person with clinically compatible mumps symptoms does not rule out mumps as a diagnosis. Successful detection of mumps virus depends primarily on the timing of collection and quality of the clinical sample. Vaccinated individuals may shed virus for a shorter period and might shed smaller amounts of virus, thus degradation of the sample has greater consequences for successful detection of virus. In outbreaks among two-dose vaccine recipients, mumps virus RNA was detected in samples from 30%–35% of case-patients if the samples were collected within the first 3 days following onset of parotitis; IgM was detected in 13%–15% of these cases (Bitsko et al. 2008; Rota et al. 2009).

Q: What does a mumps-positive RT-PCR result mean?

A: A positive RT-PCR signal indicates the presence of mumps virus RNA in the patient sample. The positive result should be used only to support a clinical diagnosis of mumps. A positive RT-PCR result provides laboratory confirmation of mumps infection in persons with symptoms consistent with mumps who have not been vaccinated within the preceding 45 days.

Q: Why attempt to isolate mumps virus in cell culture?

A: Virus isolation is considered among the best methods for confirming mumps infection. Virus can be detected when IgM antibodies or a rise in IgG titer are not detected. Often it is necessary to grow the virus in culture to have adequate material for viral sequencing. Sequence analysis allows the determination of the mumps genotype (there are currently 12 recognized genotypes). The sequence information can help to identify the source of the virus and can provide confirmation of suspected epidemiologic links. In addition, virus isolation is less likely than PCR assays to give false-positive results due to contamination.

Q: What is a mumps genotype?

A: Mumps strains are assigned to 1 of 12 genotypes on the basis of the sequence of the gene coding for the SH (short hydrophobic) protein. In some cases, a genotype has been associated with endemic circulation of mumps virus in a country or region; however, routine virologic surveillance for mumps is limited to only a few countries. The genetic information from circulating mumps viruses is used to track the transmission pathways of the virus and can be used to suggest epidemiologic links, or lack thereof, between cases and outbreaks. The Jeryl-Lynn vaccine strain is a member of genotype A, so identification of genotype A suggests an association with recent vaccination.

Q: What is the gold standard for laboratory confirmation of mumps?

A: Virus culture is the gold standard for mumps confirmation. However, sample quality must be maintained to ensure viability of the virus. Laboratories are strongly encouraged to perform cell culture isolation of mumps from buccal or oral swab specimens. Primary monkey kidney cells and Vero cells are frequently used to isolate virus. Detection of mumps in culture can be done using immunofluorescent antibody staining or standard RT-PCR.

Q: If a clinical sample is determined to be positive by RT-PCR or by viral isolation at the state laboratory, is it necessary to send a sample to CDC for sequence analysis?

A: Laboratories are encouraged to send patient samples from positive sporadic cases of mumps as well as representative samples from an outbreak. 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.

Q: Where can I find RT-PCR and real-time RT-PCR protocols for mumps?

A: The following protocols are available online:

Q: Where do I obtain material for RT-PCR and virus isolation controls?

A: 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-PCRs 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

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