Description

• Can be asymptomatic in 30% of nonimmune individuals and 60% of previously vaccinated cases
• Painful parotitis in 95% of symptomatic mumps cases
• Epidemics in late winter and spring; transmission by respiratory droplets or contact with saliva
• Incubation period is 12 to 25 days.
• System(s) affected: hematologic/lymphatic/immunologic, reproductive, skin, exocrine
• Synonym(s): epidemic parotitis; infectious parotitis

Epidemiology

• 85% of mumps cases occur prior to 15 years of age.
• Adult cases are typically more severe.
• Predominant sex: male = female
• Geriatric population: Most U.S. adults are immune.
• Acute epidemic mumps: highly contagious in susceptible populations, R0 =10
  • Most cases occur in unvaccinated children 5 to 15 years of age.
  • Multiple recent outbreaks in U.S. college students
• Mumps is unusual in children <2 years of age.
• Period of maximal communicability is 24 hours before to 72 hours after onset of parotitis.

Incidence

• Worldwide, 169,799 cases of mumps were reported in 2019. In the United States, 2019, 3474 cases of mumps were reported. In 2020, the COVID-19 pandemic year, only 616 cases were reported in the United States.
• Since 1967 (start of U.S. national vaccination program), case rate has dropped from 100/100,000 to 1.1/100,000.
• Occasional regional epidemic outbreaks

Prevalence

• 0.0064/100,000 persons in United States
• 90% of adults in the United States are seropositive.

Etiology and Pathophysiology

Mumps is an RNA virus (Rubulavirus) of the paramyxovirus genus. Mumps virus replicates in glandular epithelium of parotid gland, pancreas, and testes, leading to interstitial edema and inflammation.

• Interstitial glandular hemorrhage may occur.
• Pressure caused by testicular edema against the tunica albuginea can lead to necrosis and loss of function.

Risk Factors

• Global travel: One-third of countries in regions including Africa, South Asia, Southeast Asia, and Japan do not mandate mumps vaccination and continue to have pediatric epidemics every 4 years. Many areas of South and Central America do not have high mumps vaccine coverage. Travel from an area of recent epidemic should be noted.
• Crowded environments such as dormitories, barracks, or detention facilities increase risk of transmission. It is considered a human-only virus, but infectious viral particles have been found in bats.
• Immunity wanes rapidly after single-dose vaccination. With a 2-dose schedule, immunity drops slowly from 95% to 86% after 9 years.

General Prevention

• Vaccination
  • 2 doses of live mumps vaccine or mumps, measles, rubella (MMR, or with varicella MMR-V) vaccine recommended, first at 12 to 15 months and second at 4 to 6 years. May start early at 6 months of age if travel is planned.
  • 95% effective in clinical studies; field trials show 68–95% efficacy, which may be insufficient for herd immunity to prevent spread due to high contagiousness of mumps.
  • Prevention may require 95% first dose and >80% second-dose adherence. Vaccine failure may increase 10–27% each year after vaccination.
  • Adverse effects of vaccine: fever 8/100,000; seizure 25/100,000; thrombocytopenic purpura 3/100,000
  • No relationship between MMR vaccine and autism celiac disease or multiple sclerosis. Recent data show a reduced autism risk in girls after MMR vaccination (aHR 0.79, overall for both genders aHR 0.93) (1).
• Immunoglobulin (Ig) post exposure does not prevent mumps.
• Postexposure vaccination does not protect from recent exposure (2)[B].
• Institute respiratory droplet isolation for hospitalized patients for 5 days after onset of parotitis.
• Isolate nonimmune individuals for 26 days after last case onset (social quarantine) due to incubation period as long as 25 days.
• In an epidemic situation, a third dose of MMR is indicated to decrease the attack rate (3)[A]. The boosted immunity from a third dose only seems to last about 1 year.
• Vaccine neutralizing antibodies are still effective against variant strains of mumps virus.
• Although there are no reports of disseminated mumps from MMR vaccine in HIV patients, live vaccines (MMR) are contraindicated in immunocompromised patients (e.g., HIV with CD4 <200).

Pregnancy Considerations

• Live viral vaccines are typically contraindicated in pregnancy; however, vaccination of children should not be delayed if a family member is pregnant. MMR given to breastfeeding mothers has not shown adverse effects in their infants.
• Immunization of contacts protects against future (but not current) exposures.