Background
Mumps is a contagious viral infection caused by a paramyxovirus that spreads through droplets or saliva, typically entering through the nose or mouth. The virus can be present in saliva before symptoms appear, with the highest transmission just before the development of parotitis (swelling of the salivary glands). Mumps is less contagious than measles and mostly affects unimmunized populations, although outbreaks have occurred even among immunized individuals due to factors such as primary vaccine failure and waning immunity.
In the United States, there was a significant resurgence of mumps in 2006, primarily affecting vaccinated young adults. Since then, sporadic outbreaks have led to fluctuating annual cases, with incidents typically occurring in college campuses and close-knit communities. Mumps cases can be imported and lead to outbreaks within communities, particularly in crowded living conditions.
The peak incidence of mumps is during late winter and early spring, and although the disease can affect individuals of any age, it is uncommon in children younger than 2 years. Approximately a quarter of cases may not present with symptoms. The mumps vaccine, introduced in 1967, is effective in reducing the incidence of the disease, though occasional resurgences have been observed. [1, 2]
See the Centers for Disease Control and Prevention (CDC) recommended immunization schedule for persons aged 0-18 years, [3] the catch-up schedule for persons aged 4 months to 18 years, [4] and the adult immunization schedule for persons older than 18 years. [5]
Pathophysiology
The mumps virus is transmitted by respiratory droplets, direct contact, or contaminated fomites. It has an incubation period of 12-24 days after initial transmission. [2] After the incubation period, prodromal symptoms occur and last anywhere from 3-5 days. After the prodrome, the symptoms of the virus depend on which organ is affected. The most common presentation is a parotitis, which occurs in 30-40% of patients. Other reported sites of infection are the testes, pancreas, eyes, ovaries, central nervous system, joints, and kidneys. A patient is considered infectious from about 3 days before the onset and up to 4 days after the start of active parotitis. Infections can be asymptomatic in up to 20% of persons.
Epidemiology
Mumps occurs worldwide, with a peak incidence during late winter to early spring. Sporadic mumps outbreaks have occurred among susceptible individuals in various settings, including military posts, schools, colleges and universities, and summer camps. During outbreaks, mumps can affect vaccinated individuals, but prior immunization helps to limit the symptoms, duration, and spread of mumps.
United States
Prior to the vaccine about 50% of children contracted mumps. Approximately 200,000 cases were reported in 1964 before the introduction of the vaccine compared with 291 cases in 2005. A resurgence occurred in 1986 and 1987, with almost 13,000 cases reported, and it was associated with a lack of state requirements for immunizations. These cases were mostly in older school-aged children (10-19 y). In the 1990s, 30-40% of cases reported each year were in persons aged 15 years or older as opposed to 90% being younger than 15 years old in earlier years. [6]
An outbreak of mumps occurred in Iowa, with 219 cases reported in 2006. In addition, another 14 cases of people with symptoms consistent with the virus were reported in nearby states (Illinois, Nebraska, and Minnesota). This is the largest number of cases reported in the United States since 1988. The median age of the 219 persons was 21 years, with 30% being college students. In 1991, Iowa mandated that 2 doses of mumps vaccine be required for all people entering public schools. Vaccination history was studied in 133 people from this outbreak: 65% (87) of the patients had received 2 doses, 14% (19) had received only 1 dose, and 6% (8) received no vaccine at all. The source of the Iowa epidemic is unknown. [7]
Among the infected, the most commonly reported symptoms were parotitis (83%), submaxillary/submandibular gland swelling (40%), fever (36%), and sore throat (32%). The average length of illness was 5.1 days. Complications, including encephalitis and orchitis, were reported in 5% of patients.
International
The variations in the number of persons who receive the mumps vaccination worldwide make it difficult to estimate the numbers affected. The incidence varies markedly from region to region.
The United Kingdom reported an epidemic of mumps in 2005, with 56,390 cases reported in persons aged 15-24 years who were not vaccinated. [6]
Sex
For parotitis, males and females are affected equally.
Symptomatic meningitis has a male-to-female ratio of 3:1.
Age
Before the mumps vaccine was introduced, most cases were in children aged 5-9 years, with 90% being younger than 15 years. The resurgence in the late 1980s affected older children aged 10-19 years. In more recent years, up to 30-40% of cases have been in persons older than 15 years. [1]
Prognosis
Uncomplicated mumps generally resolves on its own, with rare cases of relapse occurring around 2 weeks later. The prognosis for patients with mumps-related meningitis is typically good, although some might experience permanent issues like nerve deafness or facial paralysis. Rare complications like postinfectious encephalitis, acute cerebellar ataxia, transverse myelitis, and polyneuritis can also occur. In most cases, children with mumps recover fully within a few weeks, with a good overall prognosis. However, mumps in adults tends to be more severe. The most severe complication is encephalitis, which carries a mortality rate of 1.5%. [8]
Mumps during pregnancy can lead to risks of embryonic or fetal death and spontaneous abortion, although malformations are not commonly reported. [8] Unilateral orchitis rarely causes sterility, but bilateral orchitis poses a higher risk. Unilateral sensorineural hearing loss is considered rare, though subclinical or undiagnosed mumps may contribute to a greater incidence of hearing loss than currently known, with documented cases of bilateral involvement. [2]
Mortality/Morbidity
Between 1980 and 1999, mumps resulted in an average of one death per year, with most fatalities occurring in individuals older than 19 years. While CNS involvement is common, symptomatic meningitis only affects 1-10% of patients and typically resolves without complications. Encephalitis, a rare occurrence in 0.1% of cases, carries a mortality rate of 1.5%. [9, 10, 11, 12, 13]
Orchitis affects 50% of postpubertal males and may lead to testicular atrophy in up to 50% of cases, particularly in bilateral orchitis where the risk of sterility is higher. [10, 14] Oophoritis is rare but can occur in a small percentage of postpubertal girls.
Pancreatitis manifests in 3% of mumps cases, with resultant transient hyperglycemia and occasional reports of diabetes mellitus. [13] Deafness, reported in 1 in 20,000 cases of mumps, often presents unilaterally. [13, 15, 16] Myocarditis-related deaths have been documented, with an incidence of up to 15%, largely asymptomatic. [17]
In women, mumps during the first trimester of pregnancy increases the risk of spontaneous abortion, although it is not associated with congenital malformations. [18] Additional complications may include chronic arthritis, arthralgias, and nephritis. [17]
Causes
Mumps is typically caused by a single-stranded RNA virus belonging to the Paramyxovirus genus. Humans serve as the only natural host for the mumps virus.
Other viruses implicated in recurrent parotitis are influenza, echovirus, parainfluenza (types 1 and 3), and coxsackievirus A. More rare causes of parotitis seen in persons with HIV infection are adenovirus or cytomegalovirus.
Risk factors include lack of immunization or incomplete immunization, international travel, and immune deficiencies.
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Child with mumps.
