Mumps Outbreak

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CDC Health Advisory

Distributed via Health Alert Network

April 14, 2006, 20:34 EDT (08:34 PM EDT)

CDCHAN-00243-06-04-14-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Department of Public Health (IDPH) (IDPH, unpublished data).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Minnesota, Missouri, Nebraska, and Wisconsin (CDC unpublished data,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

1. Centers for Disease Control and Prevention. Mumps Epidemic---

Iowa, 2006--- April 7, 2006. MMWR 2006;55(13):366-8.

2. CDC. Exposure to Mumps During Air Travel --- United States, April

2006. MMWR. 2006;

55:1-2.

3. CDC. Mumps epidemic - United Kingdom, 2004-05. MMWR 2006;55;173-

5.

4. Plotkin, SA, Orenstein WA, et al. Vaccines, 4th Edition, 2003,

p.441-5.

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.

6. Red Book: 2003 Report of the Committee of Infectious Diseases,

American Academy of Pediatrics, pp 439-443.

7. CDC. Mumps outbreak at a summer camp - New York, 2005. MMWR

2006;55:175-77.

8. Vaccine Preventable Diseases Surveillance Manual, 3rd Edition,

2002, p. 7-1 - 7-12.