Introduction

Mumps is a significant childhood infectious disease caused by the mumps virus (MuV). Due to its generally mild clinical presentation, mumps has received less attention compared to other infectious diseases like measles.¹ Historically, mumps have been highly prevalent, often leading to outbreaks in densely populated areas. Without vaccination, it typically infects children, most commonly between the ages of 5 and 9. However, in 2016 and 2017, the number of mumps cases in the United States nearly doubled compared to the previous five years, primarily among adolescents and young adults. This increase is attributed to factors such as waning vaccine immunity and opposition to vaccination.² In recent years, several large outbreaks of mumps have been reported in developed countries, posing a new public health challenge.³ Previous reports indicate that 70% of patients with a known vaccination history had received two doses of the measles, mumps, and rubella (MMR) vaccine before falling ill.⁴ Unlike mumps, cases of measles and rubella are rare in individuals who have received two doses of the MMR vaccine, suggesting that certain factors may affect the mumps vaccine's effectiveness.⁵ Therefore, understanding the epidemiology, pathogenesis, and characteristics of the mumps virus, as well as the vaccine, is crucial for protecting against the spread of MuV infection.

What are Mumps?

Mumps, a systemic viral infection, is characterized by the swelling of the parotid glands.⁶ Humans are the only natural host of the mumps virus. It is easily identified by the painful swelling on the sides of the face under the ears, which gives those affected a distinctive "hamster face" appearance.⁷ Early symptoms of mumps are non-specific and include fever, headache, malaise, muscle pain, and loss of appetite. These initial symptoms are usually followed by painful swelling around the sides of the face, known as parotitis, which is the most common symptom of a mumps infection. Symptoms typically appear 16 to 18 days after exposure to the virus. Approximately one-third of people with a mumps infection are asymptomatic.⁸

Complications from mumps are rare but can include deafness and various inflammatory conditions, with the most common being inflammation of the testes, breasts, ovaries, pancreas, meninges, and brain. Viral meningitis can occur in one-quarter of individuals with mumps. Testicular inflammation may lead to reduced fertility and, in rare cases, sterility.⁹

Diagnosis

Consideration of risk factors

History of mumps infection 

Mumps is rare in people who have previously been infected with mumps.

Immunization history

• Mumps is rare in people who have been fully immunized.
•  Young adults who have not received the full two doses of the combined measles, mumps, and rubella (MMR) vaccine are most frequently affected.

Age

Mumps rarely occur in infants aged under 1 year.

Contact with a patient with mumps 

Significant contact is defined as being in the same room for 15 minutes or more, or having face-to-face interaction. Mumps may have been contracted up to 4 weeks previously.

Recent outbreaks 

Consider reaching out to the local Health Protection Team (HPT) to check for any localized mumps outbreaks.

Clinical diagnosis

Consider a diagnosis of mumps in individuals presenting with parotitis (swollen parotid glands), which occurs in 95% of symptomatic cases:

• Typically, one parotid gland is affected first, reaching its maximum size after 2–3 days, with the other gland usually swelling shortly after. About a quarter of those affected experience unilateral parotitis.
• The earlobe over the affected gland may be pushed upward and outward, and the angle of the mandible may become obscured, unlike in cases of cervical adenopathy.
• The affected gland may be tender to touch.
• During gland enlargement, individuals may experience earache and have difficulty pronouncing words or chewing.

Other features consistent with a diagnosis of mumps include:

Non-specific symptoms, which may precede parotitis, such as headache, ear-ache, muscle ache, malaise, low-grade fever and loss of appetite. These typically occur one day before the overt signs of parotitis and peak when the parotid glands are most swollen.¹⁰

Laboratory diagnosis

Laboratory confirmation of mumps involves techniques such as reverse transcriptase-polymerase chain reaction (RT-PCR) and serum immunoglobulin M (IgM) antibodies. IgM levels peak up to eight days after symptom onset ¹¹ and can be measured by enzyme-linked immunosorbent assays (ELISA) 7–10 days after symptoms begin. At the initial presentation of a suspected mumps infection, the clinician should collect two specimens: a buccal or oral swab for RT-PCR and an acute-phase serum specimen for IgM and IgG antibodies. Buccal specimens should ideally be obtained within 3 days of parotid gland swelling, and no later than 8 days after symptom onset. Massaging the parotid gland for 30 seconds before collecting the buccal swab can enhance specimen quality.

In unvaccinated individuals, the IgM response may not be detectable until up to 5 days after symptom onset, and it may not be detectable at all in vaccinated individuals.¹² Incorrect collection of acute-phase samples can result in false-negative results; in such cases, repeat serum samples should be collected 7 to 10 days after symptom onset for accurate results. In vaccinated individuals, antibody-based diagnosis can be challenging since IgM may not be detectable in acute-phase serum samples. In such instances, MuV RNA can be identified from throat swabs, oral fluid or urine.¹¹

In cases of meningitis, MuV-specific IgM can be found in the cerebrospinal fluid (CSF) in half of the cases, and IgG in 30–90% of cases, sometimes persisting for more than a year with an elevated white blood cell count. These findings are not associated with an increased risk of long-term complications¹⁴ Most cases of parotitis show an elevated white blood cell count in the CSF.¹⁵

Clinicians treating patients with suspected or confirmed mumps should notify their local or state health authority in accordance with public health laws and regulations.

Differential diagnosis

Secondary infections that may present with parotitis include:

• Acute suppurative parotitis which is an acute bacterial infection caused by Staphylococcus aureus, and potentially by atypical mycobacteria (e.g., tuberculosis)
• Viral infections such as Epstein–Barr virus (causing mononucleosis), parainfluenza, adenovirus, influenza type A, coxsackievirus, parvovirus B19 (causing erythema infectiosum or slapped cheek syndrome), lymphocytic choriomeningitis virus, and HIV

Non-infectious causes of parotitis include:

• Metabolic disorders, including diabetes mellitus, cirrhosis, and uremia
• Autoimmune disorders, such as Sjogren's syndrome ,sarcoidosis, and granulomatosis with polyangiitis (previously known as Wegener's granulomatosis)
• Parotid duct obstruction, such as from salivary stones, cysts, or tumors
• Prescription drugs, such as iodide contrast media, phenothiazines, thiouracil, and thiazide diuretics¹⁶

Management

Prevention

Mumps is preventable through vaccination. Mumps vaccines contain live attenuated viruses and are included in the immunization programs of most countries. The MMR vaccine, which also protects against measles and rubella, is the most commonly used mumps vaccine. Protection against mumps is higher with two doses of the MMR vaccine compared to one,¹⁷ with effectiveness estimated between 79% and 95%, which is lower than the protection against measles and rubella. Nevertheless, this level of protection has been sufficient to nearly eliminate mumps in countries that vaccinate against it and to significantly reduce the frequency of complications among those vaccinated.¹⁸

^Treatment

Mumps is generally a mild benign illness that resolves on its own. Treatment mainly focuses on providing supportive care for the symptoms. Analgesic medications and cold or warm compresses can help alleviate parotid swelling. Testicular swelling and tenderness should be managed with elevation and cold compresses. There is no proven benefit for using glucocorticoids to treat mumps orchitis. ¹⁹ A therapeutic lumbar puncture may be effective in relieving headaches associated with aseptic meningitis caused by a mumps viral infection. ²⁰

Patients with mumps should follow droplet precautions and remain isolated for 5 days after the onset of parotid swelling to minimize the risk of transmission. ²¹

Prognosis

Mumps is typically a self-limiting disease that resolves within 1–2 weeks, with most individuals recovering without any long-term complications.²²

Summary

In conclusion, mumps remains a significant childhood infectious disease, often overlooked due to its typically mild clinical presentation. Recent increases in mumps cases, particularly among adolescents and young adults, underscore the importance of vaccination and heightened awareness. Diagnosis relies on careful consideration of risk factors, clinical symptoms, and laboratory confirmation techniques. While mumps is usually self-limiting and resolves within weeks, complications can occur, emphasizing the need for proper management and prevention strategies. Vigilance among healthcare providers, adherence to public health guidelines, and continued research into vaccine efficacy and disease dynamics are crucial for controlling mumps and its potential spread.