Mumps

Synonym: epidemic parotitis

Mumps is an acute, generalised infection caused by a paramyxovirus, usually in children and young adults.

• It can infect any organ but usually affects the salivary glands and, less often, the pancreas, testis, ovary, brain, mammary gland, liver, kidney, joints and heart.

• The incubation period is between 16-18 days (range 12-25 days)¹.

• The virus is highly infectious with transmission by droplets spread in saliva via close personal contact.

• It is most infectious from around 1-2 days before onset of symptoms, to about 9 days afterwards, although it may be asymptomatic in 15-20% of people.

• Asymptomatic mumps infection is common in children.

• Nearly all people develop lifelong immunity to mumps after one episode of infection. However, 1-2% of cases are thought to be re-infections.

• Infected persons excrete the virus for several days before symptoms appear and for several days afterwards.

Since the introduction of the measles, mumps and rubella (MMR) vaccine, mumps has become a notifiable disease to help monitor the effectiveness of the vaccine.

Epidemiology

Either clinical or subclinical infection used to be very common in childhood but, with the introduction of the MMR vaccine in 1987, numbers dwindled considerably. Since 2004, the majority of the confirmed cases have been linked with outbreaks in universities. Many of the cases in 2019 are the 'Wakefield cohorts' - young adults who are still unvaccinated or had only received one dose of the MMR vaccine. They are old enough to attend college and university and outbreaks are likely to continue.

Public Health England (PHE) data show that there were 5,042 lab-confirmed cases of mumps in England in 2019, compared to 1,066 cases in 2018². This is the highest number of cases since 2009.

Presentation¹

• Mumps can be asymptomatic.

• Non-specific symptoms lasting a few days, such as fever, headache, malaise, myalgia and anorexia, can precede parotitis.

• Parotitis is usually bilateral although it can be unilateral.

• Typically, there is pain at or near the angle of the jaw.

• Fever may be as high as 39.5°C without rigors in small children.

• Swelling causes distortion of the face and neck with skin over the gland hot and flushed but there is no rash.

• With severe swelling, the mouth cannot be opened and is dry because the salivary ducts are blocked.

• Discomfort lasts for three or four days but may be prolonged when one side clears and the other side swells.

• Usually just the parotid glands are involved but, rarely, the submaxillary and sublingual salivary glands are affected.

Orchitis

• Orchitis may occur four or five days after the start of parotitis but it often appears without it. This can sometimes lead to the diagnosis being missed.

• Orchitis presents with chills, sweats, headache and backache with swinging temperature and severe local testicular pain and tenderness.

• The scrotum is swollen and oedematous so that the testes are impalpable.

• Orchitis is usually unilateral but may be bilateral.

• Sometimes, as one side resolves, orchitis strikes the other side three or four days later.

• Orchitis occurs in around 25% of postpubertal men.

• Subfertility following bilateral orchitis is rare.

Meningitis and encephalitis

• Mumps frequently affects the nervous system.

• Meningism occurs in around 15% of patients³.

• It usually occurs without parotitis.

• Meningitis is usually mild and self-limiting.

• Mumps encephalitis may present early by direct invasion following initial infection, or late as a post-infectious event.

Differential diagnosis⁴

• By far the most common presentation of mumps is with parotitis. High temperature, pain and swelling in the neck are common with many other infections, including tonsillitis, viral pharyngitis and infectious mononucleosis. The tender, swollen parotid glands emerge from behind the ramus of the mandible and can be distinguished from lymph nodes in that on palpation it is not possible to feel in front of the parotid glands.

• HIV infection should be considered.

• Patients with a stone in the parotid duct tend to be older but a much more important feature is that the gland swells and becomes more painful on chewing as saliva is produced.

• Mumps must be in the differential diagnosis of viral meningitis and encephalitis.

• Mumps orchitis typically strikes at the same age as torsion of the testis. In torsion, the testis is usually still palpable with the long axis horizontal. There is no pyrexia and there are no other aches and pains.

• Rubella, drug reactions and allergic reactions should also be considered.

Investigations

• In most cases, the diagnosis can be made clinically. However, since the introduction of the MMR vaccine, all cases require laboratory confirmation. If a diagnosis of mumps is considered likely, notify the local HPU, which will arrange for an oral fluid sample to be collected for confirmation of the infection.

• In patients with meningitis but without parotitis, the diagnosis may be confirmed by detection of mumps-specific antibodies in the serum. Salivary immunoglobulin M (IgM) against mumps may be detected³. As with mumps parotitis, the local HPU will arrange oral fluid testing. Specific antibody levels may not rise for several days and so, if the result is negative but clinical suspicion is strong, it is worth repeating the test.

• Real-time reverse transcriptase polymerase chain reaction tests (RT-PCR) and mumps genotyping are useful in cases where mumps occurs in immunised patients.

• High-resolution colour Doppler ultrasound has been used to differentiate mumps orchitis from torsion.

Management

This is mainly supportive. Maintain good fluid intake and keep the mouth moist.

Drugs

• There is no specific treatment but drugs such as paracetamol and ibuprofen may give symptomatic relief.

• For mumps orchitis, treatment is initially conservative with bed rest, fluids and analgesia.

Prognosis

Most cases are self-limiting with full recovery within 1-2 weeks¹. About 1 in 1,000 people with mumps meningitis develop encephalitis, of whom 1.5% of cases are fatal⁵. Deaths from other causes are rare, with more than half the cases arising in men over the age of 19 years.

Complications

Other complications of mumps can include⁴:

• Oophoritis, which may cause pain in 5% of postpubertal females; sterility seldom occurs.

• Deafness affects about 4% of people; however, permanent deafness is much less common (about 1 in 20,000 people)¹. Bilateral hearing loss is very rare.

• Pancreatitis occurs in around 4% of cases.

• Mild upper abdominal pain (may be related to the pancreas in around 50% of cases).

• Neuritis, arthritis, nephritis, thyroiditis and pericarditis have all been reported.

• Transient and mild mastitis (uncommon - can occur in either sex).

• Mumps in the first trimester of pregnancy may increase the rate of spontaneous abortion but the virus is not teratogenic.

Prevention

• MMR vaccine is given in the national immunisation programme (see the separate Measles, Mumps and Rubella (MMR) Vaccination article)⁶.

• Normal hygiene measures to prevent droplet infection should be instituted in the household of a patient who has mumps.

• Children should be excluded from school for five days following onset of parotid swelling.