Mumps

• A highly contagious vaccine-preventable viral illness.
• Parotitis usually follows a few days of non-specific febrile symptoms. Mumps may however be only mildly symptomatic, including absence of fever.
• Parotitis may initially be unilateral, but will progress to be bilateral in 90%. Unilateral involvement therefore does not exclude mumps, but alternative causes should be considered. Firm, erythematous swelling, significant tenderness, and purulent discharge from the parotid duct suggest a bacterial cause.
• Can also involve the testicles (orchitis), ovaries (oophoritis) and the central nervous system.

• The mumps component of MMR offers around 80-90% protection after two doses, unlike the measles and rubella components, which offer close to 100%. A vaccination history therefore makes mumps less likely, but still possible.
• A number of other common viruses can sometimes cause parotitis e.g. influenza.

This varies depending on current epidemiology, with a lower threshold for testing if recent cases have been identified locally or nationally, or other possible exposure (e.g. overseas travel). If in doubt discuss with a clinical microbiologist or public health.

Request Mumps PCR

Viral buccal swab for mumps PCR (RNA) in those with parotitis

• Massage the parotid gland for 30 seconds and then swab adjacent to the parotid duct to collect saliva directly from the gland.
• Good sensitivity – a negative result on a well-collected sample within the first 3 days of parotitis makes the diagnosis unlikely. Beyond day 3 the sensitivity drops.
• Excellent specificity – a positive result confirms the diagnosis, unless recent vaccination

If a patient presents with orchitis, oophoritis, or neurological complications, discuss testing with a microbiologist, as urine or CSF samples for PCR may be helpful.

Serology is not the recommended first line test. It is sometimes used in certain situations, e.g. people beyond the window of good PCR sensitivity. However results may be uninterpretable, especially if vaccinated. Discuss with a microbiologist prior to testing.

• IgM is used to indicate acute infection, and is more likely to be detectable from day 3 of parotitis. However, it has poor sensitivity, particularly in vaccinated individuals, so a negative result cannot exclude mumps.
• IgM also has poor specificity and false positives can be seen with other illnesses.
• IgG indicates vaccination or infection with mumps at some point in time, so a positive result does not confirm current acute infection. A negative convalescent sample can however exclude mumps as a cause of illness.

• Suspicion of mumps should be notified immediately to public health
• People with suspected mumps should avoid waiting rooms, laboratory collection centres, or other areas where they could expose others to possible infection.