Description

• Asymptomatic in up to 30% of the nonimmune individuals and 60% of previously vaccinated individuals.
• Painful parotitis in 95% of symptomatic mumps cases
• Epidemics in late winter and in spring
• Transmission by respiratory droplets or contact with saliva
• Incubation period is 12 to 25 days, followed by 2 to 3 days of symptomatic phase.

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.
• 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, 3,474 cases of mumps were reported in 2019. In 2020, the COVID-19 pandemic year, only 616 cases were reported in the United States, followed by 154 cases in 2021, possibly due to social distancing or other COVID-19 preventative measures. In 2022, there were a total of 322 cases reported in the United States.
• Since 1967 (start of U.S. national vaccination program), case rate globally has dropped from 100/100,000 to 1.1/100,000.
• Occasional regional epidemic outbreaks occur among individuals who have been fully vaccinated, primarily in settings with intense or frequent close contact, such as universities and correctional facilities.

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, and rarely kidneys, 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 Africa, South Asia, Southeast Asia, and Japan do not mandate mumps vaccination and continue to have pediatric epidemics (roughly 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 show an 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 from 95% to 86% after 9 years.

General Prevention

• Vaccination is effective and essential, especially for pediatric travelers (1) and should be considered 3 months post cancer chemotherapy if antibody titers are low.
  • 2 doses of live attenuated mumps vaccine or mumps, measles, rubella (MMR, or with varicella MMR-V) vaccine are recommended, first at aged 12 to 15 months and second at aged 4 to 6 years. May start early at 6 months of age if travel is planned, but this dose does not count toward their 2-dose schedule.
  • 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 Jeryl-Lynn vaccine: seizure 25/100,000; fever 8/100,000; 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) (2).
• Immunoglobulin (Ig) post exposure does not prevent mumps. Postexposure vaccination does not protect from recent exposure.
• 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 3rd dose has been observed to last up to 3 years (4).
• The neutralizing antibodies from vaccination 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 patients 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 and MMR-V given to breastfeeding mothers have not shown adverse effects in their infants.
• Immunization of contacts protects against future (but not current) exposures.