More than 1,000 cases of mumps in nine states have been confirmed in the nation's largest mumps outbreak in decades, announced Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, Atlanta.

The outbreak began in Iowa in December 2005 among college students, whose close living conditions make them susceptible to the virus, Dr. Gerberding said in a press briefing. By comparison, a yearly average of 265 mumps cases have been reported for the entire country since 2001, while Iowa previously averaged just 5 cases per year since 1996, the CDC reported (MMWR [Dispatch] 2006;55:1–3).

“As clinicians become more aware of what we are looking for, we expect more cases will be diagnosed,” Dr. Gerberding said. “A lot of clinicians have never seen a case of mumps. Not everyone presents with swollen glands.”

Most cases occurred in people aged 18–25 years, many of whom had received either one or two doses of the mumps vaccine. Cases are under investigation in Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, and Wisconsin. Dr. Gerberding declined to name additional states in which suspected but unconfirmed cases are under investigation.

In addition, two individuals have been identified in Iowa who were potentially infectious during nine different commercial flights between March 26 and April 2, to or from cities outside the Midwest, including Tucson, Ariz.; Dallas; and Washington, the CDC said in an official health advisory issued on April 14.

Mumps, an acute viral upper respiratory infection, may present initially with nonspecific symptoms such as myalgia, anorexia, malaise, headache, and fever, and progress to acute onset of unilateral or bilateral tenderness and swelling of parotid or other salivary glands. About 30%–70% of unvaccinated people develop typical acute parotitis, but up to 20% of infections are asymptomatic; nearly 50% are associated with nonspecific symptoms or symptoms that are primarily respiratory, with or without parotitis. Severe complications can include deafness, orchitis, oophoritis, mastitis, meningitis/encephalitis, and spontaneous abortion.

Most people with mumps are ill for about a week, and they can be contagious from 3 days before symptoms appear until about 9 days after the appearance of symptoms, according to the CDC.

“It's very important for health care workers to have a second dose of the MMR vaccine,” Dr. Gerberding emphasized.

Health care providers in affected areas are advised to offer the MMR vaccine to individuals without evidence of immunity, including all unvaccinated persons born after 1957. In addition, a second dose is recommended for school-age children, college students, and other high-risk groups. Most children have received both doses, but vaccine coverage rates vary with location and population, Dr. Gerberding said.

The supply of MMR vaccine is adequate to cope with the outbreak, she said. The CDC will assist states with vaccine supplies as needed, and Merck has donated 25,000 doses to the CDC's stockpile.

The problem, Dr. Gerberding said, is a lack of complete coverage with a vaccine that is not 100% effective. About 10% of people who receive both doses simply fail to respond and remain susceptible to mumps.

Individuals suspected to have mumps should be tested and any positive cases reported immediately to local public health officials. Such individuals should be isolated for 9 days after symptom onset, the CDC advised.

Physicians should familiarize themselves with the clinical presentations of mumps, infectious disease specialist Dr. Mary Anne Jackson told this newspaper. Some patients complain of pain at the corner of the jaw, or of an earache that can be confused with otitis. Ovarian inflammation, which may occur in up to 5% of infected postpubertal females, may be confused with appendicitis.

Symptomatic meningitis, which occurs in up to 15% of cases, is associated with a lymphocytic pleocytosis (inflammatory cells in the spinal fluid) that is typical of viral meningitis, but with a low CSF glucose level. Typical summertime enterovirus meningitis is usually associated with normal or low-normal CSF glucose levels, typically around 40%–50% of peripheral glucose. With mumps meningitis, those levels might be 10%–25%. It's important to rule out bacterial meningitis, which a low CSF glucose might suggest, said Dr. Jackson, chief of infectious disease at Children's Mercy Hospital, Kansas City, Mo.

When mumps is suspected, options include culturing the nasopharynx, throat, or urine or testing for serum IgM antibodies. Standard shell vial culture could miss mumps, so ensure that your laboratory's culture will identify mumps, she advised.

At the time of the press briefing, no deaths related to the mumps outbreak had been reported, Dr. Gerberding said. “We hope the containment steps that are being taken at the state levels will help to slow things down,” she said.

Further information from the CDC is available at www.cdc.gov/nip/diseases/mumps/mumps-outbreak.htm

Iowa Mumps Outbreak Spreads to Nearby States