Mumps
Overview
•Paramyxovirus; spread via respiratory droplets and infected saliva
•Infectious from 1-2 days before symptoms until ~9 days after onset (contagious before symptomatic)
•Up to 15-20% of infections are asymptomatic; one episode confers lifelong immunity
•UK resurgence driven by 'Wakefield cohort' - young adults who missed MMR following the discredited 1998 Wakefield paper
Presentation
•Incubation period: 16-18 days (range 12-25 days)
•Prodrome (1-2 days before parotitis): fever, headache, malaise, myalgia, anorexia
•Parotitis - hallmark; painful bilateral (70-80%) swelling at angle of jaw, lifts earlobe upwards and outwards
•Stensen's duct erythema - redness/oedema at ductal opening on buccal mucosa
•Pain on chewing, worsened by acidic foods (stimulates saliva flow against obstructed duct)
•Orchitis - unilateral testicular swelling in post-pubertal males; appears 4-8 days after parotitis
Investigations
•Mumps is a notifiable disease - notify the local Health Protection Unit (HPU) within 3 days of clinical suspicion; do not wait for lab confirmation
🥇 First-line
•oral fluid (saliva) IgM testing - arranged via HPU; highest sensitivity in first few days; repeat if initially negative with high suspicion
•Serum IgM and IgG - if oral fluid unavailable; paired acute and convalescent samples increase sensitivity
•Serum amylase - elevated in parotitis and pancreatitis
•Scrotal Doppler ultrasound - to differentiate orchitis from testicular torsion
🏆 Gold standard
•RT-PCR and mumps genotyping - most sensitive, especially in vaccinated patients with atypical antibody responses
Differential Diagnosis
Parotitis differentials
| Condition | Key distinguishing features |
|---|---|
| Bacterial parotitis | Unilateral, pus from Stensen's duct, raised WCC, more systemically unwell |
| Parotid calculus | Unilateral, sudden onset with eating, afebrile, stone on ultrasound |
| EBV (mono) | Cervical lymphadenopathy, exudative tonsillitis, splenomegaly, positive Monospot |
| Testicular torsion | Sudden severe pain, no fever, no parotitis - surgical emergency; must exclude urgently |
Management
•No specific antiviral - management is entirely supportive
•Isolation for 5 days from onset of parotid swelling (away from school/work)
•Notify HPU within 3 days - statutory legal requirement
•Paracetamol or ibuprofen - analgesia and fever; adequate oral fluid intake
•Warm or cold packs to parotid region for symptomatic relief
•Orchitis: bed rest, scrotal support, paracetamol or ibuprofen - no antiviral or steroid therapy of proven benefit
Prevention
•MMR vaccine - live attenuated; two doses required for full protection
•First dose at 1 year; second dose at 3 years 4 months (pre-school booster)
•Catch-up MMR available at any age for unvaccinated individuals
•Two doses confer ~88% protection against mumps (lower than measles/rubella components - explains vaccinated outbreaks)
Complications
Key complications
Orchitis - 20-30% of post-pubertal males; usually unilateral; atrophy in ~50% affected testes; bilateral (10-30% of orchitis) → subfertility; sterility rare
Viral meningitis - ~10% of cases; often without parotitis; lymphocytic pleocytosis; usually benign
Encephalitis - ~1 in 1,000 mumps meningitis cases; case fatality ~1.5%
Sensorineural hearing loss - ~4% some deafness; permanent deafness rare (~1 in 20,000)
Pancreatitis - ~4%; epigastric pain and raised amylase; usually mild and self-limiting
Oophoritis - ~5% post-pubertal females; pelvic pain; sterility extremely rare
Mumps in pregnancy - not teratogenic but first-trimester infection increases risk of spontaneous abortion