February 2007 | Back to Table of Contents
Clinical and Health Affairs
Mumps Resurgence Promts Revised Recommendations
By Claudia Miller, M.S.
ABSTRACT
Mumps outbreaks in 2006 served as a reminder that this often-overlooked,
vaccine-preventable disease is still a threat. The outbreaks were concentrated in Iowa but affected several other states in the Midwest. As clinicians and public health officials considered Minnesota’s vulnerability to a mumps outbreak, they discovered gaps in immunization recommendations and other problems. Increased surveillance efforts uncovered the limitations of serology-based diagnostic testing for mumps. This article summarizes the epidemiology of the recent outbreaks, the issues that arose during the public health response to them, and resulting changes in recommendations for mumps prevention and control.
In December 2005, Iowa experienced the start of a mumps outbreak. A total of 1,643 confirmed cases and 315 probable cases were reported in the state by the end of September 2006.1 By comparison, an average of 265 mumps cases have been reported annually in the United States since 2001. Iowa had reported an average of 5 cases per year between 1996 and 2005. In Minnesota, a total of 22 mumps cases were reported between 2001 and 2005, with the annual incidence ranging from 1 case in 2003 to 6 in both 2001 and 2005. Of note, 10 mumps cases occurred in Minnesota between October 2005 and February 2006, suggesting an increase in mumps activity prior to receiving notice in March 2006 of the outbreak in Iowa.
The initial cases in Iowa occurred among students at a university in the eastern part of the state. The median age at onset was 22 years, and incidence peaked among 18- to 22-year-olds, although all age groups were affected. Iowa officials indicated that 22 colleges reported mumps cases related to the 2006 outbreak.
Mumps outbreaks also occurred in Kansas, Illinois, Nebraska, Missouri, South Dakota, Pennsylvania, and Wisconsin in 2006. The reason for the outbreaks is not fully known. Mumps virus from early cases was identified as genotype G, the same genotype associated with cases discovered in the United Kingdom and at a New York summer camp in 2005. In Iowa, the fact that the outbreak took place on a college campus, where students live and socialize in crowded settings, and that students had incomplete vaccine coverage (fewer than 2 doses of mumps vaccine) likely contributed to transmission of the virus.
In response to the outbreak and because of concern about interstate travel during college spring breaks, the Minnesota Department of Health issued a statewide health alert on April 6, 2006, encouraging health care providers to be vigilant about suspected mumps cases and to test patients for mumps who presented with parotid swelling. Between April and November 30, 2006, 361 suspected mumps cases were reported in Minnesota. Of those, 28 (8%) met clinical and laboratory criteria to be counted as confirmed cases; 90 (25%) were counted as probable cases, 186 (52%) were ruled out as mumps, and 57 (16%) were still under investigation. The number of suspected cases reported relative to the small number confirmed, and the large number for which the final designation was “probable” reflect the challenges of making a mumps diagnosis.
Challenges of Mumps Diagnosis and Confirmation
Mumps is an acute viral illness characterized by unilateral or bilateral tenderness and swelling of the parotid or other salivary glands lasting at least 2 days and having no other apparent cause. Mumps may start with a nonspecific prodrome that includes myalgia, anorexia, malaise, headache, and fever. Complications are rare and may include meningitis, orchitis, oophritis, mastitis, inflammation of the pancreas, and deafness.
The classic clinical presentation of mumps is not necessarily typical. In fact, only an estimated 30% to 40% of mumps infections involve parotitis. Approximately 20% are asymptomatic, and nearly half involve only nonspecific respiratory symptoms.2 Furthermore, as with all relatively rare, vaccine-preventable diseases, recognizing cases depends on a health care provider’s perception of potential disease activity in the community. Health alerts clearly raise the index of suspicion.
Laboratory confirmation of mumps is also challenging. Mumps is considered laboratory-confirmed by any of the following: a positive viral culture, a positive serologic test result for mumps IgM antibodies, or a rise in mumps IgG antibodies between acute and convalescent specimens.3
Viral culture is the gold-standard test because of its specificity; however, it lacks sensitivity, and it can take up to 14 days to grow mumps virus. Viral culture specimens are best if they come from a buccal swab (collected after massaging the gland for 30 seconds, and only if parotitis is present). Urine is the next-best source. Throat swabs, throat washings, nasal swabs, and nasal washings are acceptable but not preferred.
Timing of specimen collection is also an issue. Swabs should be performed within the first 5 days of symptoms, whereas urine should be collected 4 to 9 days after onset of symptoms to minimize the possibility of false-negative results. Serologic testing is much faster; however, appropriate timing of specimen collection for serologic testing is critical and challenging. Mumps IgM antibodies usually can be detected by the 4th day of illness and peak about 1 week after onset of symptoms. Serum for acute IgG should be obtained as early as possible; however, to avoid unnecessary blood draws, 1 specimen for acute IgM and acute IgG should be collected on or after the 4th day of swelling (or presentation of other symptoms if no swelling is present). A positive mumps IgG from a specimen collected early in the illness may indicate immunity or early infection and therefore should not be used to rule out mumps. For the convalescent IgG, blood should be drawn between 3 and 5 weeks after onset of symptoms but no sooner than 2 weeks after blood was drawn for the acute IgG. Ideally, the same laboratory should perform acute and convalescent IgG testing, preferably as paired sera.
The validity of mumps serologic test results is compromised by problems with both sensitivity and specificity. Persons with viral infections such as Epstein-Barr virus and human parainfluenza may have false-positive mumps IgM results because of cross-reactivity. In addition, mumps IgM antibodies may be transient or absent in persons with mumps who have previously received mumps vaccine. This is especially problematic in a highly vaccinated population in which individuals who contract the disease do so because of vaccine failure—when vaccination fails to prevent the disease—rather than because they weren’t vaccinated. A demonstrated rise in IgG antibodies from serum specimens collected during the acute and convalescent phases of the illness is more reliable; however, patients rarely are persuaded to return to the clinic for a convalescent blood draw.
In Minnesota, suspect cases were confirmed only if the mumps viral culture was positive, a significant rise in mumps IgG antibodies between acute and convalescent specimens was demonstrated, or a positive mumps IgM result was reported in a patient who presented with parotid swelling that lasted at least 2 days. Cases in which a person suspected of having mumps also had another diagnosis such as mononucleosis or parainfluenza were ruled out.
Updated Mumps Vaccination Recommendations
In response to measles outbreaks among adolescents and young adults during the 1980s, the national Advisory Committee on Immunization Practices (ACIP) recommended in 1989 that all school-aged children receive 2 doses rather than 1 of the combined measles, mumps, and rubella (MMR) vaccine. That same year, Minnesota colleges began requiring students to have at least 1 dose of the MMR vaccine. In 1992, the state began requiring a second dose of MMR for students entering grade 7 or 12, unless those students were legally exempt. In 2004, the state changed the law and began requiring the second dose prior to students’ entering kindergarten. As a result, most Minnesotans are immune to mumps. Those who are most susceptible are infants older than 6 months of age who have not yet received their first dose of mumps vaccine and for whom maternal antibody has waned and persons 35 through 44 years of age who may have received a single dose of a less-than-optimal vaccine and have not had the disease.
In 1998, the ACIP issued recommendations for the control and elimination of mumps. Those recommendations included having a first dose of MMR vaccine at 12 to 15 months of age, and a second dose at 4 to 6 years of age.4 Two doses of MMR vaccine also were recommended for students attending college and other post-high school institutions. In addition, national guidelines from the ACIP and the Hospital Infection Control Practices Advisory Committee published in 1997 recommended that health care workers receive 1 dose of mumps and rubella vaccine and 2 doses of measles vaccine.5 Because of the focus on measles and rubella immunity, documentation of immunity to mumps was often not included in their employee health record. For that reason, prior to the 2006 mumps resurgence, the immune status of college students and health care workers to mumps was largely unknown.
|
Table
Key Changes to 1998 ACIP Recommendations on Mumps Immunization
Acceptable Presumptive Evidence of Immunity
Documentation of adequate vaccination is now 2 doses of a live mumps virus vaccine instead of 1 dose for
• School-aged children (grades K-12)
• Adults at high risk (persons who work in health care facilities, international travelers, and students at post-high school educational institutions)
Routine Vaccination for Health Care Workers
• Persons born during or after 1957 without other evidence of immunity: 2 doses of a live mumps virus vaccine
• Persons born before 1957 without other evidence of immunity: consider recommending 1 dose of a live mumps virus vaccine
During Outbreaks
• Children ages 1 to 4 years and adults at low risk: if affected by the outbreak, consider a second dose of a live mumps virus vaccine (note: minimum interval between doses=28 days)
• Health care workers born before 1957 without other evidence of immunity: strongly consider recommending 2 doses of live mumps virus vaccine. |
In response to the mumps outbreak, the Centers for Disease Control and Prevention informally recommended that all health care workers in states where outbreaks occurred receive 2 doses of mumps vaccine. The ACIP published this recommendation in June of 2006 (Table), stating that routine vaccination for health care workers should include 2 doses of mumps vaccine for persons born during or after 1957 without other evidence of immunity (ie, physician-diagnosed mumps or serologic evidence of the disease) and 1 dose of mumps vaccine for persons born before 1957.
5 Recognizing the challenge these changes presented for health care facilities, the Minnesota Department of Health issued mumps guidelines for health care facilities, encouraging them to begin moving toward including mumps in health care worker immunization programs by requiring 2 doses of MMR vaccine.
Discussion
Vaccines represent one of the top public health success stories of the 20th century. Immunization as a disease-prevention strategy is challenged, however, when vaccine-preventable diseases occur in persons who are appropriately vaccinated for their age and when outbreaks occur among highly vaccinated groups or populations. In Iowa, 884 (49%) of the 1,798 persons with confirmed and probable mumps investigated as of September 30, 2006, reported having received at least 2 doses of MMR vaccine, and an additional 245 (14%) reported having received at least 1 dose. This led many to question the efficacy of mumps vaccine.
Considering that mumps vaccine efficacy demonstrated in clinical trials is 95% (range: 90% to 97%), the number of mumps cases reported in Iowa did not necessarily indicate that the vaccine is ineffective. For example, if mumps were introduced into a group of 100 vaccinated persons, approximately 5 (range: 3 to 10) would be expected to develop mumps infection. Once mumps was introduced into college campuses in Iowa (a total of 22 colleges reported cases during the 2006 outbreak), the crowded conditions associated with dormitory living led to a large number of exposures that resulted in transmission. The attack rates on 2 highly affected campuses were 2.0% and 3.8%. Ninety-seven percent and 77% of students on those campuses, respectively, had received 2 doses of MMR vaccine. The vaccine failure rate among dormitory roommates was 10% (1/10) among those having received 1 dose of mumps vaccine, and 8% (7/84) among those having received 2 doses.
Vaccines are not 100% effective. The success of immunization programs depends on 2 strategies: maximizing immunity in the population in order to minimize disease introduction and transmission, and implementing public health interventions to minimize exposure such as social distancing (any effort to limit social contact), decrease case infectiousness (eg, antimicrobial treatment of pertussis cases), or prevent disease in people who have contact with someone who is infected (eg, administering measles postexposure vaccination and or immune globulin). In order to prevent the transmission of mumps, the only public health intervention known to be effective is social distancing—an intervention that is
most difficult to implement in a college setting.
Conclusion
The Iowa mumps outbreak of 2006 demonstrated that despite a high rate of immunization, vaccine-preventable diseases can occur in clusters and large outbreaks can occur when conditions are conducive to transmission. The resurgence also highlighted the importance of disease surveillance and ongoing evaluation of immunization and other disease-prevention and control strategies. MM
Claudia Miller supervises the Minnesota Department of Health’s Vaccine-Preventable Disease Surveillance Unit.
The mumps incidence data included in this article were collected by a team of state and local public health agency epidemiologists, including epidemiologists from the Minnesota Department of Health Field Services Section and the Local Epidemiology Network of Minnesota. Minnesota Department of Health epidemiologist Cynthia Kenyon coordinated the mumps investigations and compiled and summarized the data with assistance from Gary Wax and Kim Moore. The author also acknowledges the Iowa Department of Public Health staff for their work on the mumps outbreak.
References
1. Iowa Department of Public Health, Center for Acute Disease Epidemiology. Iowa Mumps Update Through Saturday, September 30, 2006. Available at http://www.idph.state.ia.us/adper/common/pdf/mumps/mumps_update_093006.pdf. Accessed January 3, 2007.
2. Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Hamborsky J, MicIntyre L, Wolfe S, eds. 9th ed. Washington, DC: Public Health Foundation 2006.
3. Centers for Disease Control and Prevention. Mumps—Laboratory Testing for Mumps Infection. Available at: http://www.cdc.gov/nip/diseases/mumps/faqs-lab-test-infect.htm. Accessed January 3, 2007.
4. Centers for Disease Control and Prevention. Measles, mumps, and rubella—vaccine use and strategies for elimination of measles, rubella, and congenital rubella syndrome and control of mumps: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR. 1998;47(No. RR-8):1-57.
5. Centers for Disease Control and Prevention. Immunization of health-care workers: recommendations of the Advisory Committee on Immunization Practices (ACIP) and the Hospital Infection Control Practices Advisory Committee (HICPAC). MMWR. 1997;46(RR-18):1-42.
6. Centers for Disease Control and Prevention. Notice to readers: updated recommendations of the Advisory Committee on Immunization Practices (ACIP) for the control and elimination of mumps. MMWR. 2006;55(22):629-30.