Mumps - Characteristic Presentation and Treatment

The Pathogen

Transmission and Incubation

• Spreads by direct contact with respiratory droplets or saliva from an infected person
• Incubation period: 12-25 days (average 16-18 days)
• Infectivity window: 2 days before to 5 days after onset of parotitis; virus detectable in saliva up to 7 days before and 9 days after onset
• Virus can also be isolated from urine and seminal fluid up to 14 days after parotitis onset
• Humans are the only known natural reservoir

Clinical Presentation

Prodrome (1-2 days before parotitis)

• Low-grade fever
• Malaise
• Myalgia
• Anorexia
• Headache

Cardinal Sign: Parotitis

• Parotid gland swelling is the hallmark - occurs in ~95% of symptomatic cases
• Typically starts unilaterally, then progresses to bilateral involvement in most cases
• The gland is tense and painful, but erythema and warmth are notably absent (distinguishing from suppurative parotitis)
• Stensen's duct may appear inflamed, but no pus can be expressed
• Swelling typically lasts 1-5 days
• Can obscure the angle of the mandible
• Submandibular and sublingual glands may also be affected
• Up to 20% of infections are subclinical (asymptomatic)

Complications

Orchitis (most clinically significant in males)

• Occurs in 20-30% of postpubertal males (rare before puberty); usually unilateral but bilateral in ~15-30% of orchitis cases
• Presents with fever, chills, headache, nausea, and testicular pain/swelling - typically 4-8 days after parotitis
• Testicular atrophy follows in ~50% of affected testes, but bilateral atrophy causing sterility is rare (~13% of cases with bilateral orchitis)
• Neither glucocorticoids nor incision of the tunica albuginea are of proven value

Oophoritis / Mastitis

• Oophoritis: ~7% of unvaccinated postpubertal women; presents with lower abdominal pain and vomiting
• Mastitis: up to 30% of unvaccinated postpubertal women; much less common in vaccinated individuals

Pancreatitis

• ~4% of unvaccinated patients; <1% of vaccinated patients
• Elevated serum amylase can reflect either parotitis or pancreatitis; elevated serum lipase helps distinguish pancreatitis

CNS Involvement

• Subclinical CNS involvement (CSF pleocytosis) occurs in up to 55% of patients
• Aseptic meningitis: up to 10% of unvaccinated; ≤1% of vaccinated patients. Self-limited, presents ~5 days after parotitis with stiff neck, headache, drowsiness. Can precede parotitis or occur without parotitis in 40-50% of cases
• Encephalitis: ≤1% of patients; presents with high fever, altered consciousness, seizures (20-30% of CNS cases), focal neurologic signs. Mortality ~1.5%; permanent sequelae possible
• Other CNS manifestations: cerebellar ataxia, facial palsy, transverse myelitis, hydrocephalus, Guillain-Barre syndrome

Hearing Loss

• Up to 4% of unvaccinated patients; <1% of vaccinated patients
• Usually sudden onset, unilateral, and transient; bilateral permanent hearing loss is rare
• Results from viral damage to the cochlea (organ of Corti and tectorial membrane)

Cardiac

• ECG abnormalities in up to 15% of cases (usually transient)
• Rare: myocarditis, endocardial fibroelastosis

Other

• Thyroiditis, nephritis, arthritis, hepatic disease, keratouveitis, thrombocytopenic purpura, hemolytic anemia

Diagnosis

• Primarily clinical in typical presentations
• Lab confirmation indicated for atypical cases, vaccinated individuals, and outbreak investigations
• Buccal swab or urine for RT-PCR (preferred during first 3 days of parotitis)
• Serology: IgM and IgG mumps antibodies (note: IgM may be absent in vaccinated individuals)
• Elevated serum amylase reflects parotid/pancreatic inflammation

Treatment

• Mumps immune globulin is NOT recommended for post-exposure prophylaxis or treatment
• Patients should be isolated (droplet precautions) for 5 days after onset of parotitis
• Children should be excluded from school for 9 days after onset of parotid swelling
• Immunocompetent patients with isolated parotitis or orchitis can be managed as outpatients; admit for systemic complications (encephalitis, severe pancreatitis)

Prevention

• MMR vaccine (2-dose schedule): first dose at 12-15 months, second dose at 4-6 years
• A third dose of MMR has been recommended by the CDC during active outbreaks in high-risk settings (colleges, close-knit communities)
• Vaccine efficacy: ~79-88% per dose; two doses provide ~88% protection
• Disease is milder in vaccinated individuals who do become infected