Brief Report: Update: Mumps Activity --- United States, January 1--October 7, 2006

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During January 1--October 7, 2006, a total of 45 states* and the District of Columbia reported 5,783 confirmed or probable mumps cases to CDC (Figure). This includes 2,597 cases previously reported by 11 states during January 1--April 29, 2006 (1). This report summarizes the epidemiology of mumps cases in the United States during 2006. With low levels of reported mumps continuing, health-care workers should remain alert to suspected mumps, conduct appropriate laboratory testing, and use every opportunity to ensure adequate immunity, particularly among populations at high risk for mumps.

Cases of mumps are reportable through the National Notifiable Diseases Surveillance System (NNDSS). Reports are transmitted electronically via NNDSS to CDC each week and include individual case information such as age, sex, date of symptom onset, vaccination status, and complications of illness. Mumps cases included in this report are those with onset from January 1 (week 1) through October 7, 2006 (week 40).

The clinical case definition of mumps is an illness with acute onset of unilateral or bilateral tender, self-limited, swelling of the parotid or other salivary gland, lasting 2 or more days, and without other apparent cause. A confirmed case of mumps is one that is laboratory confirmed or meets the clinical case definition and is linked epidemiologically to a confirmed or probable case. A probable case meets the clinical case definition but is neither laboratory confirmed nor linked to another confirmed or probable mumps case (2).

Of the 5,783 cases, 3,113 (54%) were confirmed, and 2,612 (45%) were probable; for 58 cases (1%), classification was unknown. Six states reported 84% of the cases: Iowa (1,968), Kansas (904), Wisconsin (750), Illinois (591), Nebraska (357), and South Dakota (288).

For 5,747 (99%) of the 5,783 mumps cases with patient age available, the median age was 22 years (range: 1 month--96 years). Among the 5,739 (99%) patients for whom sex was known, 3,644 (63%) were female. As reported previously (1), the highest age-specific rate continues to be among persons aged 18--24 years, many of whom were college students.

Data regarding vaccination status are incomplete. In Iowa, one of the states with the most complete data, preliminary vaccination data have been reported through September 30. Among 1,798 patients with completed follow-up reports, 123 (7%) were unvaccinated; 245 (14%) had received 1 dose of measles, mumps, and rubella (MMR) vaccine, and 884 (49%) had received >2 doses of MMR vaccine. The vaccination status of 546 (30%) patients, the majority of whom were adults, was unknown (3).

Among the 5,783 cases for which weeks of onset are known, cases peaked during April 16--29, the onset period for 1,498 (26%) cases (Figure). The number of reported cases decreased during May--September, when most students were not attending college. However, since students began returning to school in August, mumps clusters have been reported from three college or university campuses in Illinois (84 cases), Kansas (22 cases), and Virginia (12 cases). Most of these cases (96%) were reported in persons who had received 2 doses of MMR vaccine. Because 2 doses of mumps-containing vaccine are not 100% effective, in a setting with high vaccination coverage such as the United States, most mumps cases likely will occur in persons who have received the 2 doses. Multiple other factors might have contributed to the spread of the mumps outbreak (e.g., the close-contact environment of college dormitories or varying college admission requirements for MMR vaccination) (1).

Health-care providers should continue to remain alert for suspected mumps cases, conduct appropriate diagnostic testing, and report these cases to local or state health departments. At the initial visit, recommended specimens for laboratory testing include serum to test for mumps immunoglobulin M (IgM) antibodies and a swab from the parotid duct or other affected salivary gland ducts for viral isolation, reverse transcriptase--polymerase chain reaction testing, or both. Parotid duct swab is the preferred viral sample for mumps; urine samples are no longer recommended. The first (acute) serum specimen should be collected within 5 days of illness onset. If the IgM antibody titer is negative, a second (convalescent) serum specimen for IgM antibodies is recommended 2--3 weeks after onset of signs (e.g., parotitis) or symptoms; a delayed IgM response has been observed in patients with confirmed cases of mumps, especially in vaccinated persons. The paired serum specimens also can be used to detect a significant rise (as defined by the testing kit instructions) in immunoglobulin G (IgG seroconversion) if measured by enzyme-linked immunosorbent assay or a fourfold rise in titer if measured using plaque-reduction neutralization assays or similar quantitative assay. Negative laboratory tests, especially in vaccinated persons, should not be used to rule out a mumps diagnosis, because these tests are not sensitive enough to detect infection in all persons with clinical illness. In the absence of another diagnosis, cases meeting the clinical case definition should be reported as mumps cases.

In response to this nationwide mumps outbreak, ACIP recommendations for prevention and control of mumps were updated (4). Evidence of immunity through documentation of vaccination is now defined as 1 dose of live mumps vaccine for preschool-aged children and adults not at high risk for exposure and infection and 2 doses of live mumps vaccine for school-aged children (i.e., grades kindergarten--12) and adults at high risk for exposure and infection (i.e., health-care workers, international travelers, and students at post--high-school education institutions). Additional recommendations for outbreak control include administering a second dose of MMR for preschool children and adults not at high risk for exposure and infection if these persons are part of a group that is experiencing an outbreak (4). To ensure high levels of immunity, especially among groups at high risk for exposure and infection, every opportunity should be used to provide the first or second dose of MMR vaccine to those without adequate evidence of immunity (e.g., documentation of vaccination). Private health-care providers, clinics, health departments, health-care institutions, schools, universities, and colleges should consider offering MMR vaccine through such settings as routine preventive health services and special immunization clinics, including providing MMR in conjunction with influenza vaccine.

Reported by: S Reef, MD, G Dayan, MD, W Bellini, PhD, A Barskey, MPH, S Redd, D Bi, MS, P Rota, PhD, J Rota, MPH, Div of Viral Diseases, National Center for Immunization and Respiratory Diseases (proposed), CDC.

References

* Five states (Connecticut, Delaware, Maine, Montana, and Vermont) did not report any cases to CDC.

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