Chapter 318. Mumps

Mumps is a communicable systemic viral illness usually characterized by parotitis. With the widespread use of mumps vaccine, the disease has become less common. A significant number of infections are asymptomatic.

Epidemiology

Humans are the only known natural hosts of mumps virus. The virus can be recovered from patients with active disease from saliva, cerebrospinal fluid (CSF), urine, blood, breast milk, and infected tissue.1,2 Mumps virus infections are spread by respiratory droplet or by direct contact with infected saliva. Virus can be demonstrated in respiratory secretions up to 7 days before through 9 days after the onset of parotitis.2 Secondary attack rates of mumps among susceptible household contacts have been shown to be less than that of measles or varicella, suggesting a less efficient transmission of the mumps virus.3 The normal incubation period is from 16 to 18 days (range 12–25 days). In susceptible, unimmunized populations, 60% to 70% of infections are associated with parotitis.4 However, there is a substantial subclinical attack rate produced by the mumps virus. Approximately 20% of mumps infections may go unrecognized, especially in adults, because they do not have evidence of parotitis.2,5 Given the number of subclinical cases, information regarding a patient’s history of mumps infection is notoriously inaccurate. Mumps virus infection is most communicable from 1 to 2 days prior to parotid swelling until 5 days after parotid swelling begins.2 Introduction of infection onto a hospital ward in areas where vaccine is not routinely given may lead to widespread nosocomial transmission because some patients may develop subclinical infection, and patients are contagious prior to onset of parotid swelling, making it extremely difficult to prevent transmission.6

Introduction of an effective, live-attenuated virus vaccine (Jeryl Lynn strain) in 1967, combined with the introduction of school laws regarding mumps vaccination, led to a marked reduction in the number of reported cases of mumps in the United States, from more than 185,000 cases in 1968 to 2982 in 1985.7 Following a brief resurgence of disease, a revised recommendation for two doses of measles-mumps-rubella (MMR) vaccine in 19894 and subsequent changes in school laws requiring two doses of vaccine, the annual number of mumps cases further declined. From 2001 to 2005, fewer than 300 cases of mumps were reported annually in the United States.8 In 2006, a multistate mumps outbreak with more than 5700 cases, many involving older adolescents and young adults, demonstrated that although two doses of vaccine were more protective than a single dose, protection from infection, even with two doses of vaccine, was not 100%.5,9 Outside the United States, mumps remains endemic in many countries throughout the world.10,11 In 2005, only 57% of World Health Organization member-countries reportedly used mumps vaccine.11

A single attack of mumps is believed to confer permanent immunity against a subsequent attack, regardless of whether the patient had evidence of parotitis. Mumps antibody is transferred across the placenta and persists during the first several months of the infant’s life. Similar to measles, infants born to mothers who had mumps disease may have higher antibody titers than those infants born to mothers who received immunization and did not have disease.

Pathophysiology

Mumps is caused by a paramyxovirus, which is closely related antigenically to parainfluenza virus. Virons are approximately 150 nm and contain RNA. Mumps virus can be propagated in a variety of cell cultures and in embryonated eggs. Mumps virus produces a generalized, systemic infection. Although parotid involvement has been emphasized, mumps can definitely occur without parotid swelling. Meningitis and renal involvement may be considered part of the disease. A majority (50–60%) of infected persons have cerebrospinal fluid (CSF) pleocytosis, even in the absence of clinical signs of meningitis. Adults, and males, are at greater risk of developing meningitis than are children.2,7 Of note, boys more frequently have meningitis than girls.2 Viruria occurs frequently in cases of uncomplicated mumps; hematuria and proteinuria may occur, and abnormalities of renal function have been reported. Although orchitis is a known complication of postpubertal males and may lead to some degree of testicular atrophy, sterility is rare.16,17 Oophoritis is relatively uncommon (5%) in postpubertal females. Other organs may be involved infrequently. Death due to mumps virus is rare; fatalities are more frequent in those older than 19 years. In such rare patients, virus has been recovered from multiple organs at autopsy.

Clinical Manifestations

A patient with mumps rarely has severe systemic manifestations. Temperatures are only moderately elevated, usually for 3 to 4 days. Symptoms such as headache, anorexia, and abdominal discomfort may precede parotid swelling by 1 to 2 days. Parotid swelling may be the first sign of illness; swelling may last 7 to 10 days and be observed on one or both sides (Fig. 318-1). Two or 3 days after the onset of swelling on one side, the opposite side may become involved. The submandibular glands may swell along with or in the absence of parotid swelling. Presternal edema is sometimes present.

The entire parotid gland is swollen, including the uncinate lobe, which extends under the back of the ear lobe. The borders of the gland are usually not discrete. Pressure on the parotid gland causes pain, and trismus (spasm of the masticator muscles) may occur.

Parotid swelling produces a fair amount of discomfort. Eating or drinking acidic foods, such as orange juice, is said to elicit much discomfort. Inflammation of the orifice of the Stenson duct may or may not be present.

Older patients with mumps frequently complain of headache, which probably represents involvement of the meninges. Other signs of meningeal irritation may also be present, although fewer than 10% have symptoms of central nervous system infection.7 Evidence of encephalitis, such as convulsions or disturbances of mentation, occurs rarely.

Anorexia is a frequent complaint. Some patients may complain of abdominal pain, which may represent involvement of the pancreas or of the ovaries in the female. Serum amylase is usually elevated during the infection. In severely ill patients, vomiting may be a significant problem.

A substantial portion of patients with mumps infection will go unrecognized. They may have fever and other systemic symptoms of illness. Mumps meningitis may occur in the absence of parotid swelling.

Complications

The most feared complication of mumps in males is orchitis. Although this is seen most frequently in postpubertal males, orchitis has been reported in children as young as 3 years of age. From 14% to 35% of persons who have mumps develop orchitis. The highest rate of orchitis is observed in those 15 to 29 years of age.17

The onset of orchitis is usually heralded by fever toward the end of the first week of illness. There is severe pain, swelling, and tenderness; tenderness may persist for weeks. Orchitis may also occur before or in the absence of parotitis. The involvement is most often unilateral, but bilateral involvement has been reported to occur. Atrophy may occur after orchitis. Unilateral atrophy will not result in sterility, but bilateral orchitis may.16 Development of malignancies in affected testes has been reported.17 Appropriate therapy for orchitis includes use of analgesics and adequate support of the testes. Application of ice has occasionally been useful.

In addition to involvement of testis, other glands may occasionally be involved; oophoritis, mastitis, and pancreatitis may occasionally accompany mumps. Mastitis is estimated to occur in 31% of females older than 15 years with mumps.7 Oophoritis is usually manifested by emesis, fever, and lower abdominal pain. Involvement of the thyroid has also been reported.

Mumps virus is neurotropic. Meningitis or meningoencephalitis occurs with mumps virus infection more commonly than encephalitis. Symptoms of central nervous system (CNS) involvement typically occur 3 to 10 days after the onset of parotid gland swelling. Lethargy, nuchal rigidity, and vomiting are common.

Cerebrospinal fluid (CSF) usually contains normal or slightly elevated protein, normal or slightly decreased glucose, and pleocytosis. Cells are usually predominantly lymphocytic with the counts ordinarily under 500 cells/μL. Counts of more than 1000/μL, however, are not rare. Virus can be isolated from CSF during the first few days of meningoencephalitis.

Infection of the CNS is usually self-limited, and cases of meningitis generally have a favorable prognosis. Encephalitis may result in some permanent sequelae or even death. Hydrocephalus, retrobulbar neuritis, and paralysis, developing following mumps infection, have been described.7

Deafness is a complication associated with mumps occurring in approximately 1 per 20,000 reported cases.4 It is often unilateral. The exact frequency is difficult to ascertain. In a prospective study of hearing impairment following mumps in Finnish Army personnel, about 4% of patients had acute deafness.7 Higher tone frequencies tend to be affected most severely. The onset is sudden and results in permanent damage to patient’s hearing. Deafness is not related to CNS involvement.

Diabetes mellitus has been reported to occur after onset of mumps. Mumps virus may invade the pancreas and can infect beta cells in vitro. Pancreatic damage has never been documented in cases of diabetes mellitus occurring after mumps disease or vaccination.7 Joint involvement is an uncommon complication of mumps that is very rare in children. Large joints, especially the knees, are most frequently affected; involvement may be multiple or monoarticular. Complete recovery is usual, but symptoms may be protracted.

Mumps in pregnant women has been reported to be associated with an increased rate (25%) of fetal wastage in the first trimester.18 There is no evidence that mumps virus infection produces congenital malformations.19 Although it was once postulated that subendocardial fibroelastosis might be associated with fetal mumps infection, mumps virus does not appear to cause other types of myopathy.7 Maternal mumps near term has resulted in transmission to the newborn infant. Mumps virus has been isolated from breast milk.

Diagnosis

With a decrease in the numbers of cases of mumps in the United States following the introduction of an effective vaccine, many health care providers have not seen cases of mumps and have become less likely to suspect mumps in patients presenting with parotits.8

When confronted with an infant, child, or adolescent with bilateral or unilateral parotid swelling, a differential diagnosis should, in addition to mumps, include drug effects, metabolic diseases, systemic lupus erythematosus, parotid duct obstruction, and other infectious agents, both bacterial and viral.2 Parotid swelling has been reported in infants and children with HIV infection. Bacterial infection of the parotid gland may be accompanied by purulent discharge from the Stenson duct. The approach to neck masses is discussed in Chapter 373.

Confirmation of the diagnosis of mumps infection depends on (1) the isolation of virus in culture or detection by reverse transcriptase-polymerase chain reaction (RT-PCR), (2) by demonstrating a significant rise in specific IgG antibodies to mumps virus antigens over time, or (3) by identifying mumps-specific IgM antibody.9 The virus can be readily isolated in culture from throat swabs obtained 48 hours before to 7 days after parotid swelling begins. Virus has also been isolated from urine and cerebrospinal fluid (CSF). RT-PCR can be highly useful in detection of virus from clinical specimens.20-22 Antibodies to parainfluenza viruses may occasionally interfere with complement fixation and hemagglutination inhibition assays for mumps antibody. A negative serologic test in an immunized individual does not eliminate the diagnosis of mumps because of the test’s insensitivity to detect infection in all persons with clinical illness.9 In an immunized individual, the serologic response may be delayed and the period of virus excretion shortened.9 The mumps skin test is inaccurate and should not be used to test for immunity.

Treatment

Conservative therapy is indicated in the treatment of mumps. Adequate attention to hydration and alimentation is essential. Patients may have difficulty with acidic foods, such as orange juice. The diet should be light, with a generous offering of fluids.

Analgesics may occasionally be necessary for severe headache or discomfort caused by parotitis. Stronger analgesics may be needed for orchitis. It is unusual for vomiting to be severe enough to require intravenous fluids. In these instances, however, electrolytes lost by vomiting should be replaced.

Prevention

Mumps vaccination is discussed in Chapter 244. After a single dose of vaccine, antibodies develop in 95% to 98% of all those susceptible.7

Based on the Centers for Disease Control and Prevention (CDC) 2006 recommendations,24 children and adults can be considered to have presumptive evidence of immunity to mumps if (1) they have documentation of physician-diagnosed mumps, (2) they have documentation of vaccination with one dose of live mumps virus vaccine on or after their first birthday for preschool children and adults not at high risk and two doses for school-age children and adults at high risk, (3) they have laboratory evidence of mumps immunity, or (4) they were born before 1957. Adults at high risk are defined by the CDC as persons who work in health care facilities, international travelers, and students at post–high school educational institutions.24

Immunoglobulin is not effective in preventing mumps infection after an exposure and is not recommended. Based on a review of several studies, which included culture and/or reverse transcriptase-polymerase chain reaction (RTPCR) data, the AAP, HICPAC, and CDC now recommend a shorter isolation period of 5 days after the onset of parotitis in mumps patients, in both community and health care settings.27