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Mumps Case Investigation & Outbreak Control

Information on this page was adapted from the Manual for the Surveillance of Vaccine-Preventable Diseases (4th Edition, 2008), Chapter 9: Mumps (chapter removed while being revised)


Case Investigation

Essential components of the case investigation include the following:

Establishing a diagnosis of mumps. Because clinical diagnosis of mumps may be unreliable, cases of mumps should be laboratory confirmed. Not all cases of parotitis, especially sporadic ones, are due to mumps infection; however, mumps is the only known cause of epidemic parotitis. Experience indicates that case investigations combined with laboratory testing will result in many suspected mumps cases being discarded.

Obtaining accurate, complete immunization histories. Mumps case investigations should include complete immunization histories that document any doses of mumps-containing vaccine. Recent outbreaks of mumps have occurred among older children and adults, many who had already received at least one dose of mumps-containing vaccine. All vaccination histories should be verified by documentation of administration of two doses of live mumps-containing vaccine. Verbal history of receipt of mumps vaccine is not considered adequate proof of vaccination.

Identifying the source of infection. Efforts should be made to identify the source of infection for every confirmed case of mumps. Case-patients should be asked about contact with other known cases. When no history of contact with a known case can be elicited, opportunities for exposure to unknown cases should be sought. After determining when and where transmission likely occurred, investigative efforts should be directed to locations visited.

Assessing potential transmission and identifying contacts. As part of the case investigation, the potential for further transmission should be assessed, and contacts of the case-patient during the infectious period (3 days before until 9 days after onset of parotitis) should be identified.

Obtaining specimens for virus isolation. Efforts should be made to obtain clinical specimens (buccal, nasopharyngeal or oropharyngeal swabs, urine) for viral isolation for all cases. As the outbreak progresses, the recommendation to laboratory confirm all cases can be re-evaluated.

Virus may be isolated from the buccal mucosa from 7 days before until 9 days after parotitis and from urine during the period from 6 days before to 15 days after the onset of parotitis. Optimal specimen collection is within 5 days of symptom onset.

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Outbreak Control

Mumps is the only known cause of epidemic parotitis. The main strategy for controlling a mumps outbreak is to define the at-risk population and a transmission setting, and to rapidly identify and vaccinate susceptible persons or, if a contraindication exists, to exclude susceptible persons from the setting to prevent exposure and transmission.

Mumps vaccine, preferably as MMR, should be administered to susceptible persons. Although mumps vaccination has not been shown to be effective in preventing mumps in persons already infected, it will prevent infection in those persons who are not infected. If susceptible persons can be vaccinated early in the course of an outbreak, they can be protected. However, cases are expected to continue to occur among newly vaccinated persons who are already infected for at least 3 weeks Following vaccination because of the long incubation period for mumps.

As with all vaccines, there are some individuals who will not gain immunity after receipt of mumps vaccine. Because vaccine effectiveness is not 100%, a second dose of mumps containing vaccine is recommended during outbreak situations for individuals who have received only one dose previously. Studies have shown a trend toward a lower attack rate among children who have received two doses of mumps vaccine as opposed to those who have received one dose. Furthermore, birth before 1957 does not guarantee mumps immunity, and in outbreak settings vaccination with a mumps containing vaccine should be considered for those born before 1957 who may be exposed to mumps and who may be susceptible.

Exclusion of susceptible students from schools affected by a mumps outbreak (and other, unaffected schools judged by local public health authorities to be at risk for transmission of disease) should be considered among the means to control mumps outbreaks. Once vaccinated, students can be readmitted to school. Students who have been exempted from mumps vaccine for medical, religious, or other reasons should be excluded through at least 25 days after the onset of parotitis in the last person with mumps in the affected school.

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