ARCHIVED - Guidelines for the Prevention and Control of Mumps Outbreaks in Canada
5.0 Laboratory Guidelines for the Diagnosis of Mumps
The clinical and laboratory diagnosis of mumps can be difficult. Proper specimen collection and transportation, along with appropriate laboratory testing and cautious interpretation of results, are important in determining a mumps diagnosis. This section is based on recent experiences in mumps diagnostics in both Canada and the United States. A comprehensive description of mumps diagnostics can be found in the Manual of Clinical Microbiology(7).
Of the currently available tests, reverse transcriptase polymerase chain reaction (RT-PCR) is preferred for mumps virus detection. A summary of the laboratory diagnostics for mumps is shown in Table 5. The full version of the laboratory guidelines for the diagnosis of mumps (revised in 2007) can be found in Appendix 4.
Buccal swab or collection of saliva from the buccal cavity for reverse transcriptase polymerase chain reaction (RT-PCR) assay collected within the first 3–5 days of symptom onset is the preferred specimen. Buccal specimens should be collected using a swab approved for virus isolation and placed in virus transport media. Swabs may be dacron, nylon, and rayon tipped, and either flocked or non-flocked. Calcium alginate swabs are not acceptable, as they inhibit PCR reactions. Charcoal swabs or swabs in Ames media used for swabbing for bacterial pathogens (such as group A Streptococcus) are not acceptable. Swabs with wooden or aluminum shafts are also not acceptable.
Mumps virus has been detected in the urine by culture up to 14 days after the onset of symptoms. However, experiences in the Nova Scotia and U.S. outbreaks suggest that mumps virus cannot be detected in the urine with the same sensitivity as in oral specimens.
The first (acute) serum specimen should be collected as soon as possible upon presentation with mumps symptoms. A second (convalescent) serum specimen should be collected at least 10 days (ideally) and up to 3 weeks after the first sample.
Testing for mumps-specific IgM-class antibody has suboptimal sensitivity for the diagnosis of acute mumps in a partially immunized population (may be detectable in only 30% of acute cases). In addition, without an established epidemiologic link to a confirmed case or without travel history to an area with known/likely mumps activity, one should be cautious of false-positive IgM results.
Seroconversion (i.e., negative to positive result) or a fourfold or greater rise in titre between the acute and convalescent sera is indicative of an acute mumps infection.
The presence of mumps-specific IgG, as determined using an enzyme immunoassay (EIA), does not necessarily predict the presence of neutralizing antibodies and, thus, immunity. Conversely, the absence of detectable mumps IgG using EIA may reflect the lower sensitivity of the EIA in comparison to a more sensitive assay, such as a neutralization assay, in which IgG may be detectable.
The RT-PCR assay is reliable for the definitive diagnosis of mumps infection, but its sensitivity can be influenced by the following:
Only molecular methods (i.e., genotyping) can be used to distinguish between vaccine and wild types of the virus.
Virus genotyping is useful for differentiating vaccine and wild-type strains, linking cases, linking outbreaks, tracking importations, and documenting the elimination of a particular strain from a geographic area.
|Interpretation of laboratory results||
Testing by RT-PCR and IgM-class antibody detection is not sufficiently sensitive to rule out mumps infection, particularly if the specimen was collected 4–5 days after symptom onset.
In order to properly interpret laboratory results and to assess the performance of mumps diagnostic assays, both clinical and epidemiologic information need to be considered along with the laboratory information (e.g., prior vaccination history, travel history, timing of sample collection relative to onset of symptoms). Therefore, communication and information sharing between public health and the laboratory are essential.
|NML services||Mumps virus detection, isolation, and genotyping are available at the National Microbiology Laboratory. The online guide to services is available at http://www.nml-lnm.gc.ca/english/guide/default.asp.|
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