Apr 19, 2006 (CIDRAP News) – The nation's largest mumps epidemic in decades has reached well over 1,000 cases and will probably grow further before it ebbs, the head of the Centers for Disease Control and Prevention (CDC) said today.
Calling the epidemic the largest in more than 20 years, CDC Director Dr. Julie Gerberding said it has grown to 815 cases in Iowa and 350 cases in seven other states. Suspected cases are under investigation in seven additional states, she said. Most of the cases are in 18- to 25-year-olds, many of them college students, the CDC has said.
"We will not be surprised if we see more people affected either in the college context or as students spend time with their families or their community friends," which could lead "more extension [of mumps] into the community," Gerberding said in a teleconference this afternoon.
At least 20 people have been hospitalized in the epidemic so far, but none have died of the viral illness, Gerberding said. The illness typically involves swelling of the salivary glands along with fever, headache, malaise, muscles aches, and loss of appetite.
The CDC said last week that many of the young adults who have contracted mumps had previously been vaccinated. Today Gerberding cited two likely reasons for the epidemic: some people received only one dose of the vaccine instead of the recommended two doses, and the vaccine simply isn't effective in about 10% of recipients.
"We have no information to suggest there's any problem with the vaccine," she said. "The problem here is lack of complete coverage with the vaccine. . . . There's a group of students, mainly college students, who are less likely to have received both doses of the vaccine." The CDC says one dose of measles-mumps-rubella (MMR) vaccine protects against mumps in about 80% of people.
In addition, Gerberding said, "Though this is a very good vaccine, it 's not perfect. About 10% of people who get both doses still remain susceptible" to mumps.
When people live in crowded settings, such as college dorms or other institutions, a case of mumps can trigger "a cascade of transmission," she added.
People who were born before 1957 are considered immune to mumps, because nearly everyone in that age-group had the illness, according to the CDC.
For younger people, coverage with two doses of vaccine is important, and especially so for students, others living in institutions, and healthcare workers, Gerberding said.
Referring to healthcare workers, she said, "If you haven't received two doses, it's very important that you get your second dose."
Gerberding said the CDC has some MMR vaccine on hand and plans to supply 25,000 doses to Iowa. In addition, the vaccine manufacturer, Merck, has donated 25,000 doses, which the agency will use to immunize people in affected areas. The CDC is not expecting a shortage for now, she said.
In response to a question, she said there is no sign that waning immunity is a factor in the epidemic. If waning immunity were the primary problem, there would be more cases in older people, she said.
The source of the outbreak is unknown, according to the CDC. The strain circulating in the United States is genotype G, the same as the strain circulating in the United Kingdom, where more than 100,000 cases have occurred in the past few years, Gerberding said. But at this point there is no proof that the situations are linked, she said.
Besides Iowa, states involved in the outbeak include Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, and Wisconsin, the CDC said in its Apr 14 health advisory.
In an Apr 7 report, the CDC said the United States has had an average of 265 mumps cases per year since 2001. Gerberding said about 20% of cases are mild or asymptomatic, so people can spread the virus without knowing they have it.
The CDC says complications of mumps can include deafness, pancreatitis, meningitis, encephalitis, spontaneous abortion, and inflammation of the testicles, ovaries, or breasts. Aside from deafness, these are more likely in adults than children.
CDC. Exposure to mumps during air travel—United States, 2006. MMWR 2006 Apr 11;55(Dispatch):1-2
CDC. Mumps epidemic—Iowa, 2006. MMWR 2006 Apr 7;55(13):366-8