Introduction
Mumps is a vaccine-preventable viral disease characterized by swelling of the salivary glands; serious complications (e.g., meningitis, encephalitis, orchitis, or oophoritis) can occur. On September 29, 2011, the California Department of Public Health (CDPH) confirmed by polymerase chain reaction (PCR) three cases of mumps among students recently evaluated at their university's student health services with symptoms suggestive of mumps. An investigation by CDPH, student health services, and the local health department identified 29 mumps cases. The presumed source patient was an unvaccinated student with a history of recent travel to Western Europe, where mumps is circulating. The student had mumps symptoms >28 days before the onset of symptoms among the patients confirmed on September 29. Recognizing that at least two generations of transmission had occurred before public health authorities were alerted, measles, mumps, and rubella (MMR) vaccine was provided as a control measure. This outbreak demonstrates the potential value of requiring MMR vaccination (including documentation of immunization or other evidence of immunity) before college enrollment, heightened clinical awareness, and timely reporting of suspected mumps patients to public health authorities.
On August 25, 2011, the presumed source patient, an unvaccinated male, aged 21 years, arrived at the university's student health services with fever and unilateral facial and jaw swelling. The initial diagnosis was cellulitis and antibiotics were prescribed. By day 6 after symptom onset, the patient complained of testicular pain, and mumps was suspected. He had not been vaccinated against mumps and had traveled to Western Europe during the exposure period. He was referred for mumps serological testing, but did not follow through. His illness was not reported to the local health department when mumps was suspected. Approximately 3 weeks later, a second student, the source patient's roommate, was treated at student health services for fatigue and unilateral pain and swelling of the jaw and neck. This patient, a male aged 21 years, with a history of receiving 2 doses of MMR vaccine, received a diagnosis of parotitis. Mumps serologies were drawn, and he was advised to isolate himself in his room for 5 days. Mumps immunoglobulin M (IgM) testing was negative, and immunoglobulin G testing was positive, a pattern that does not rule out acute mumps because the ability to detect IgM is poor in vaccine recipients. The local health department was not notified. When three subsequent cases of mumps were confirmed by PCR on September 29 at CDPH, an investigation was initiated.
During the outbreak period (August 25, 2011–January 7, 2012), investigators identified 29 cases that met the Council of State and Territorial Epidemiologists 2010 case definition of mumps.* The outbreak period extended from the symptom onset date of the source patient through two incubation periods after the symptom onset of the last laboratory-confirmed case. The average incubation period for mumps is 16–18 days (range: 12–25 days); thus, the timing of the first five patients indicated that at least two generations of transmission had occurred by the time public health was notified. Case-finding activities included notifying health-care providers serving the affected community, requesting PCR testing for persons with clinically compatible symptoms, and alerting adjacent local health departments to notify CDPH of suspected mumps cases.
All patients had epidemiologic links to the university: 27 (93%) were students, one was a close contact of a student, and one was a public health staff member who assisted during a mumps vaccination clinic. Among the 29 cases, 13 (45%) were laboratory confirmed by PCR, one was confirmed by the presence of mumps IgM, and the remainder were confirmed on the basis of symptoms clinically compatible with mumps together with epidemiologic links to the university (Figure). Of the epidemiologically linked cases, 11 were negative and four were not tested by PCR. All viral specimens were genotype G, the predominant mumps genotype circulating in Western Europe. Eight patients (28%), including the source patient, were students who participated in organized sports. Four of the first five patients resided in congregate housing, and 17 (59%) illnesses occurred among students living in congregate housing. Among the 29 cases, 22 (76%) mumps illnesses occurred among persons previously vaccinated with the recommended 2 doses of MMR vaccine ( Table ).
Figure 1.
Number of mumps cases (n = 29) at a university, by week of illness onset, and mass vaccination clinics — California, 2011
* Defined as a patient associated with the university and with signs and symptoms consistent with mumps.
† Defined as detection of virus by polymerase chain reaction or by the presence of serum mumps immunoglobulin M.
CDC recommendations for mumps outbreak control include defining the at-risk population and transmission setting, and rapidly identifying and vaccinating persons without presumptive evidence of immunity.[1] Other recommended control measures include cough etiquette, respiratory and hand hygiene, and isolation of infectious patients for 5 days. Early in the outbreak, the university arranged alternate housing to isolate infectious patients who resided in congregate housing; however, as the number of patients increased, this became less feasible. Students were encouraged to monitor themselves for mumps symptoms and symptomatic students were encouraged to go to student health services for testing.
Initially, the disclosure of patient student medical records to public health authorities was limited by requirements of the federal Family Educational Rights and Privacy Act (FERPA).† Because student medical records are considered educational records under FERPA, the university requested that CDPH declare the mumps outbreak an emergency, thereby permitting public health review of student medical records.
Of approximately 36,000 students enrolled at the university; an estimated 9,300 reside in housing owned by, operated by, or affiliated with the university. Recognizing that at least two generations of transmission had occurred before public health authorities were alerted to this outbreak, and wanting to avert a larger outbreak, the local health department and the university, in consultation with CDPH and CDC, decided to provide MMR vaccine as a control measure. The university recommends that matriculating students receive 2 doses of MMR vaccine, but does not require proof of MMR vaccination before matriculation, making student vaccination status difficult to assess. Therefore, messages sent to the university community advised that an additional dose of MMR vaccine, irrespective of previous MMR vaccination status, was recommended for all university community members, with an emphasis on those residing in congregate housing. Beginning 1 week after the local health department was alerted, five vaccination clinics were held during a 4-week period; a total of 3,631 persons received a dose of MMR vaccine.
* Additional information available at https://www.cdc.gov/vaccines/vpd-vac/mumps/outbreak/case-def.htm.
† Additional information available at https://www2.ed.gov/policy/gen/guid/fpco/index.html.
Morbidity and Mortality Weekly Report. 2012;61(48):986-989. © 2012 Centers for Disease Control and Prevention (CDC)
