Immunization, Vaccines and Biologicals

WHO-recommended surveillance standard of mumps

Rationale for surveillance

Mumps, caused by a paramyxovirus, is generally a mild disease with fever, headache and swelling of the salivary glands, but complications such as meningitis (in up to 15% of cases), encephalitis or orchitis may occur. Although the case-fatality rate of mumps encephalitis is low and overall mortality is 1/10 000 cases, permanent sequelae occur in about 25% of encephalitis cases. Mumps is a leading cause of acquired sensorineural deafness among children, affecting approximately 5/100 000 mumps patients. Mumps infection during the first 12 weeks of pregnancy is associated with a 25% incidence of spontaneous abortion, although malformations following mumps virus infection during pregnancy have not been found

In the pre-vaccination era mumps was the main cause of viral encephalitis in many countries. By 2002 mumps vaccine was included in the routine immunization schedule of 121 countries/territories. In countries where vaccination was introduced and high coverage was sustained the incidence of the disease has dropped tremendously and circulation has stopped. In countries where vaccination was not introduced the incidence of mumps remains high, mostly affecting children aged 5-9 years

Surveillance for mumps should evolve with the level of control and should be adjusted to match country-specific objectives. In countries achieving high routine mumps coverage and with low incidence that includes periodic outbreaks, surveillance should be used to identify high-risk populations and predict and prevent potential outbreaks. Countries having the objective of completely interrupting mumps transmission require intensive case-based surveillance to detect, investigate and confirm every suspect mumps case in the community


Recommended case definition

Clinical case definition

Acute onset of unilateral or bilateral tender, self-limited swelling of the parotid or other salivary gland, lasting two or more days and without other apparent cause

Laboratory criteria for diagnosis

Isolation of mumps virus from an appropriate clinical specimen*
or
Seroconversion or significant (at least fourfold) rise in serum mumps IgG titre as determined by any standard serological assay**
or
Positive serological test for mumps-specific IgM antibodies**

*Mumps virus can be isolated from throat swabs, urine and cerebrospinal fluid (CSF). Although mumps viral culture is rarely performed in uncomplicated cases the virus is readily isolated from CSF in cases of mumps meningitis. In research settings, typing methods are available to distinguish wild-type mumps virus from vaccine virus. All commercially available mumps vaccines are based on live attenuated strains of the virus. In general, adverse reactions to mumps vaccination are rare and mild. Vaccine-related mumps meningitis, however, has been known to occur with some vaccine strains
**In the absence of mumps immunization in the preceding six weeks

Case classification

Clinical case: A case that meets the clinical case definition
Laboratory-confirmed: A case that meets the clinical case definition and is laboratory-confirmed
Epidemiologically confirmed: A case that meets the clinical case definition and is linked epidemiologically to a laboratory-confirmed case


Recommended types of surveillance

When mumps is endemic, only routine monthly reporting of aggregated data of clinical mumps cases is recommended by district, age group and immunization status. Only outbreaks (not each case) should be investigated

When a high level of control is achieved (i.e. sustained high vaccine coverage), case-based surveillance should be conducted and every case should be reported and investigated immediately (and also included in the weekly or monthly reporting system). Suspected mumps outbreaks should be confirmed by conducting laboratory investigation on 5-10 cases only. In specific situations, viral isolation can be attempted to differentiate meningitis cases that could be related to the wild virus, the vaccine strain or other factors

Designated reporting sites at all levels should report at a specified frequency (e.g. weekly or monthly) even if there are zero cases (often referred to as "zero reporting")


Recommended minimum data elements

Aggregated data reporting

  • Number of cases by age group and immunization status, month and geographical area

Case-based data

  • Unique identifier
  • Geographical area (e.g. district and province)
  • Date of birth
  • Sex: 1 = male; 2 = female; 9 = unknown
  • Date of onset
  • Number of mumps vaccine doses received: 99 = unknown
  • Date of receipt of last dose
  • Date of notification
  • Date of case investigation
  • Date of blood specimen collection
  • Date blood specimen sent to laboratory
  • Date mumps serology results reported
  • Results of mumps serology: 1 = positive; 2 = negative; 3 = indeterminate; 4 = no specimens processed; 9 = unknown
  • Collection of specimen for viral culture/identification: 1 = yes; 2 = no; 9 = unknown
  • Specimen type: 1 = urine; 2 = throat swab; 3 = CSF; 9 = unknown
  • Date specimen received for viral culture/identification
  • Results of mumps viral culture/identification: 1 = positive; 2 = negative; 9 = unknown
  • Final classification: 1 = clinically confirmed; 2 = laboratory-confirmed; 3 = epidemiologically linked to laboratory-confirmed case
  • Source of infection identified: 1 = yes; 2 = no; 9 = unknown

Recommended data analyses, presentations, reports
  • Number of cases and incidence rate by month, year and geographical area
  • Mumps vaccine coverage by year and geographical area
  • Completeness/timeliness of monthly reporting
  • Proportion of known outbreaks confirmed by the laboratory
  • Age-specific, sex-specific, and district-specific incidence rates by month and year
  • Proportion of cases by age group and immunization status. Core age groups suggested: < 12 months, 1-4 years, 5-9 years, 10-14 years, 15-19 years, 20 years and over

Principal uses of data for decision-making

Countries where mumps is endemic

Monitor incidence and coverage to assess progress (i.e. decreasing incidence and increasing coverage) and to identify areas at high risk or with poor programme performance. Describe the changing epidemiology of mumps. Monitor vaccine effectiveness. Detect and investigate outbreaks to ensure proper case management and determine why outbreaks occurred (e.g. failure to vaccinate, vaccine failure or accumulation of susceptibles despite high vaccine coverage with effective vaccine).

Countries with high level of control

Monitor the epidemiology (age groups at risk, interepidemic period, immunization status) of mumps and accelerate immunization activities accordingly to avert a potential outbreak


Special aspects

Where vaccine is used and high coverage is achieved the monitoring of vaccine-associated mumps meningitis and its differenciation from meningitis due to other causes can be an important issue. The monitoring of mumps meningitis, wether related to vaccine or natural disease, can be integrated into overall meningitis surveillance activities.

The vast majority of mumps vaccine is used in combination with measles and rubella vaccines (MMR), and surveillance strategies for mumps should take surveillance for measles, rubella and congenital rubella syndrome into consideration.


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