Approach
According to the US guidelines, diagnosis of mumps is based on clinical presentation, history, and laboratory test results.[28] Clinical diagnosis may be made when a patient has a typical case of parotitis; however, all suspected cases should be confirmed with serology, culture, or polymerase chain reaction (PCR).[29]
History
Mumps infection begins usually with a prodrome of low-grade fever, malaise, headache, myalgias, and anorexia.[2] Parotid swelling is present in 95% of people with symptomatic mumps and usually lasts 5 days.[1][30] In the post-vaccine era, most mumps cases occur in young adults and college students.
In countries without mumps vaccination, children are the most commonly affected age group.[3] It is important to ascertain a vaccination history. Fully vaccinated people can contract the disease, but are at much lower risk for both mumps and its complications.[1]
Complications associated with mumps include orchitis, oophoritis, aseptic meningitis, encephalitis (approximately 0.1% of people with mumps), mastitis, and deafness (usually unilateral).[1] They can occur in the absence of parotitis, potentially delaying diagnosis of the disease.
Investigations
All suspected cases of mumps should be confirmed with laboratory testing.[29] Laboratory testing is also useful in atypical presentations without parotitis.
CBC
Typically, the WBC count and differential are normal. However, leukocytosis has been seen in mumps meningitis, orchitis, or pancreatitis.[2]
Serology
Serum IgM testing should not be performed earlier than 3 days following the onset of clinical symptoms, with the ideal timing for IgM testing suggested as 7-10 days postsymptom onset.[31] A positive mumps IgM test indicates a very recent infection.[32] The test will usually remain positive for up to 4 weeks. However, false-negative results may occur in people with acute mumps infection who were vaccinated previously.[33] A negative IgM titer in a previously vaccinated person does not rule out acute infection, because IgM is not a major constituent of the secondary immune response. If the initial IgM is negative in a vaccinated person, a second specimen should be collected in case a delayed IgM response has occurred.[32]
IgG serology for mumps is diagnostic if there is a 4-fold rise between acute and convalescent phase titers in IgG antibody levels. The acute titer should be drawn approximately 4 days after the onset of original symptoms. The convalescent sample should be drawn 2-3 weeks after the onset of symptoms. A 4-fold rise demonstrated by quantitative assay or a seroconversion from negative to positive in enzyme immunoassay is considered diagnostic.[32] This increase might not be observed in vaccinated people; therefore, a negative test does not rule out mumps infection.[2]
Saliva testing
Salivary mumps IgM testing is also possible. The pattern of response and accuracy is very similar to that for serum IgM.[34]
Polymerase chain reaction (PCR) assays
The use of PCR enables a more rapid and accurate confirmation of mumps. Testing is done directly on the clinical specimen, preferably saliva. A reverse transcriptase PCR (RT-PCR) assay using a small specific gene fragment can confirm infection, identify the specific viral strain, and advance epidemiologic studies.[2]
In comparison studies, RT-PCR was shown universally to be more sensitive than viral culture techniques.[2] In one study of people with a clinical diagnosis of viral CNS disease, mumps virus was detected by RT-PCR in the CSF of 96% of patients, whereas only 39% of patients had positive CSF cultures by immunohistochemical staining.[35]
Viral culture
Selective viral isolation has limited success because mumps virus replication is transient. The virus has been isolated frequently from the CSF, saliva, urine, or seminal fluid during the first week of clinical symptoms; successful viral isolation declines significantly after the first week.[2] The presence of the virus is detected by immunofluorescence staining of the sample.
Although viremia is common, isolation of the mumps virus from the blood is rare and typically only possible within the first 2 days of illness.[36] The inability to isolate mumps virus in the blood may be secondary to the coincident presence of antibodies to the virus.[2]
Serum amylase
The level may be elevated in parotitis and mumps pancreatitis (of which symptoms include abdominal pain, chills, fever, and persistent vomiting), but the test is nonspecific.[2]
If neurologic complications are suspected (e.g., severe headache, clouding of consciousness, focal neurologic signs), CSF analysis and CT scans of the head can be used to rule out other pathology.
CSF
Imaging
CT of the head can be used as an initial test if there are focal neurologic symptoms, including sensory or motor abnormalities, vision changes, or cognitive abnormalities.
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