Friday, April 14, 2006, 20:34 EDT (08:34 PM EDT)
CDCHAN-00243-2006-04-14-ADV-N
Multi-state Mumps Outbreak
The state of Iowa has been experiencing
a large outbreak of mumps that began in December 2005 (1). As of April 12,
2006, 605 suspect, probable and confirmed cases have been reported to the Iowa
Department of Public Health (IDPH) (IDPH, unpublished data). The majority of cases are occurring among
persons 18-25 years of age, many of whom are vaccinated. Additional cases of mumps, possibly linked
to the Iowa outbreak, are also under investigation in eight neighboring states,
including Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska,
and Wisconsin (CDC unpublished data, April 14, 2006).
In addition, the Iowa Department
of Public Health has identified two persons diagnosed with mumps who were
potentially infectious during travel on nine different commercial flights
involving two airlines between March 26, 2006 and April 2, 2006. The origin and
arrival cities for these flights include Cedar Rapids and Waterloo, IA; Dallas,
TX; Detroit, MI; Lafayette, AR; Minneapolis, MN; St. Louis, MO; Tucson, AZ; and
Washington, D.C. (2).
The source of the current US
outbreak is unknown. However the mumps strain has been identified as genotype
G, the same genotype circulating in the United Kingdom (UK). The outbreak in the UK has been ongoing from
2004 to 2006 and has involved > 70,000 cases. Most UK cases have occurred among unvaccinated young adults
(3). The G genotype is not an unusual
or rare genotype and, like the rest of known genotypes of mumps, it has been
circulating globally for decades or longer.
Mumps clinical manifestations and
transmission
Mumps is an acute viral
infection characterized by a non-specific prodrome including myalgia, anorexia,
malaise, headache and fever, followed by acute onset of unilateral or bilateral
tender swelling of parotid or other salivary glands (4). In unvaccinated
populations, an estimated 30-70% of mumps infections are associated with
typical acute parotitis (4, 5).
However, as many as 20% of infections are asymptomatic and nearly 50%
are associated with non-specific or primarily respiratory symptoms, with or
without parotitis (4).
Complications of mumps infection
can include deafness, orchitis, oophoritis, or mastitis (inflammation of the
testicles, ovaries, or breasts respectively), pancreatitis, meningitis/encephalitis,
and spontaneous abortion. With the
exception of deafness, these complications are more common among adults than
children (4).
Transmission of mumps virus
occurs by direct contact with respiratory droplets, saliva or contact with
contaminated fomites. The incubation period is generally 16-18 days (range
12-25 days) from exposure to onset of symptoms (4, 6). Mumps virus has been
isolated from saliva from between two and seven days before symptom onset until
nine days after onset of symptoms (4, 6).
Mumps Prevention
The principal
strategy to prevent mumps is to achieve and maintain high immunization
levels. The Advisory Committee on
Immunization Practices (ACIP) recommends that all preschool aged children 12
months of age and older receive one dose of
measles-mumps-rubella vaccine (MMR) and all school-aged children receive
two doses of MMR, and to ensure that all adults have evidence of immunity
against mumps (5). As noted below, two doses of mumps vaccine are more
effective than a single dose.
Consequently, during outbreaks and for at-risk populations, ensuring
high vaccination coverage with two doses is encouraged. For example, health care workers may be at increased risk of acquiring
mumps and transmitting to patients and thus should receive two doses of MMR
vaccine or provide proof of immunity. Since vaccination is the cornerstone of
mumps prevention, public and private health entities concerned about spread of
mumps in a population can review the vaccination status of populations of
interest and work to address gaps in vaccination.
Mumps Vaccine
Effectiveness
Data from
outbreak investigations have shown that the effectiveness of MMR against mumps is approximately 80%
after one dose and limited data suggest effectiveness of approximately 90%
after two doses. Available evidence
suggests that mumps vaccination should provide immunity against the genotype G
virus responsible for the current US outbreak.
A study of a 2005 New York outbreak that began with imported disease
from the UK (7), demonstrated vaccine effectiveness in the expected range for
both one and two doses (New York, unpublished data). However, since the vaccine is not 100% effective, some cases can
occur in vaccinated persons. When a
highly-vaccinated population is exposed to disease, most cases of disease would
be expected to be among vaccinated persons.
Mumps vaccine has not been shown to be effective in post-exposure
prophylaxis and an interval of 2-4 weeks after vaccination may be required for
the vaccine's full immunogenicity to be achieved. For these reasons, and because of the mumps' incubation period of
12-25 days, during an outbreak, newly-vaccinated persons may develop mumps
disease as long as a month after vaccination (4, 5).
Control
of mumps outbreaks
The main strategies for
controlling a mumps outbreak are to define the at-risk population and
transmission setting, identify and isolate suspected cases, and to rapidly
identify and vaccinate susceptible persons or, if a contraindication to MMR
vaccine exists, to exclude susceptible persons from the setting to prevent
exposure and transmission. Specific
strategies are listed below.
1.
Offer
MMR vaccine to persons without evidence of immunity. Evidence of immunity includes physician diagnosis or laboratory
evidence of mumps infection, birth before 1957 or one dose of MMR vaccine. For pre-school aged children, the first MMR
dose should be administered as close to age 12 months as possible. Although
birth before 1957 is usually considered proof of immunity, during an outbreak,
vaccination can be considered for this age group if the epidemiology of the
outbreak suggests that they are at increased risk of disease. Since two doses of MMR vaccine is more
effective than one dose for preventing mumps, a second dose of MMR vaccine is
recommended for the following groups: health care workers, school-aged children,
students at post-high school educational institutions and other age groups
considered at high risk of exposure (5, 8).
2.
Surveillance
for mumps should be enhanced in all affected areas for persons with parotitis
or other salivary gland inflammation.
Enhanced surveillance should continue for 50 days (two times the maximum
incubation period) after the date of illness onset in the last identified
case. CSTE approved case definitions
and case classifications for mumps are available (5).
3.
Persons
with suspected mumps should be tested and reported immediately to local public
health officials. Information on
collection and testing of clinical specimens for mumps will be available by
Monday April 17, 2006 at http://www.cdc.gov/nip/diseases/mumps/mumps-lab.htm.
Testing is essential as not all cases of parotitis are mumps, although
mumps is the only known cause of epidemic parotitis.
4.
Persons
suspected of having mumps should be isolated for nine days after symptom onset
(5, 6). In health care settings, the
use of respiratory precautions is recommended (5).
5.
Exclusion
of persons without evidence of immunity to mumps from institutions such as
schools and colleges affected by a mumps outbreak (and other, unaffected institutions
judged by local public health authorities to be at risk for transmission of
disease) should be considered. Once
vaccinated, students can be readmitted to school. The period of exclusion for those that remain unvaccinated should
be for at least 25 days after the onset of parotitis in the last person with
mumps in the affected institution (5, 6).
Additional information on mumps and the
prevention and control of mumps outbreaks, including vaccination, can be found
at the following website:
http://www.cdc.gov/nip/diseases/mumps/mumps-outbreak.htm.
References
- Centers for Disease Control and
Prevention. Mumps Epidemic---Iowa, 2006--- April 7, 2006. MMWR
2006;55(13):366-8.
- CDC. Exposure to Mumps During Air
Travel --- United States, April 2006.
MMWR. 2006;55:1-2.
- CDC. Mumps epidemic - United
Kingdom, 2004-05. MMWR
2006;55;173-5.
- Plotkin, SA, Orenstein WA, et al.
Vaccines, 4th Edition, 2003, p.441-5.
- CDC. 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(RR-8);1-57.
- Red Book: 2003 Report of the
Committee of Infectious Diseases, American Academy of Pediatrics, pp
439-443.
- CDC. Mumps outbreak at a summer
camp New York, 2005. MMWR
2006;55:175-77.
- Vaccine Preventable Diseases
Surveillance Manual, 3rd Edition, 2002, p. 7-1 7-12.
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