An unusual outbreak of mumps that began last month among college students in Iowa is prompting renewed calls for young people to make sure they've had the recommended two doses of the mumps vaccine.
"The college kids in Iowa were in pre-school in the time when the second dose wasn't required there," said Dr. Julia A. McMillan, professor of pediatrics at the Johns Hopkins University School of Medicine. "So there's a relatively large number ... who didn't get their second dose, 20 percent of whom would be susceptible to mumps."
Public health officials say a second dose of the mumps vaccine typically provides protection to 90 percent of the people vaccinated, compared with 80 percent of those who had only a single dose.
If there is alarm in the public health community about the current outbreak, McMillan said, it's not about mumps. "We're not talking about an infection that kills people," she said.
"The reason for the alarm is that it's an indication that the public health system hasn't been taken as seriously as it should have been," she said. "And this [mumps outbreak] is what happens when we don't comply with the recommendations that have been made."
Iowans have reported at least 630 confirmed or "probable" cases of mumps since the outbreak began. Most victims have been between the ages of 18 and 25.
Vaccine manufacturer Merck & Co. has donated 25,000 doses of mumps vaccine, and mass immunization clinics are planned for next week for young adults in Iowa.
The disease has also spread to at least seven other Midwest and Plains states, from Nebraska to Indiana, adding 350 confirmed and probable cases, according to the U.S. Centers for Disease Control and Prevention.
"We are not going to be surprised if there are more cases in more states, just given the nature of mumps and the way this outbreak is progressing," Dr. Julie L. Gerberding, the CDC Director, said at a briefing this week.
Authorities are investigating additional cases in a total of 15 states. This is the largest mumps epidemic in the United States in more than 20 years, Gerberding said.
Epidemiologists have identified two people who might have been contagious while on commercial flights to nine cities, including Washington, D.C. But neither has been linked to a mumps case in Maryland.
"We've had cases in Maryland this year, but we haven't been able to connect any to the Midwest outbreak," said John Hammond, a spokesman for the Maryland Department of Health and Mental Hygiene. Since the late 1990s, Maryland has typically seen 8 or 9 cases of mumps each year, he said.
State and local health authorities in Maryland this week issued mumps health alerts, asking health care workers to be alert for symptoms and isolate suspected cases until the diagnosis can be confirmed.
Health officials are also urging a second mumps vaccination for any health care workers, school-aged children and college students who haven't had it.
Mumps is a viral infection that's about as contagious as the common cold and spread in much the same way - through sneezing, coughing and the sharing of objects that carry saliva.
Those infected are contagious for three days before they show symptoms, and for nine days afterwards. "In addition to that, 20 percent never have symptoms, but they are contagious," McMillan said.
Symptoms include fever, headache, muscle aches, fatigue and loss of appetite. Then the salivary glands begin to swell, producing the illness' characteristic chipmunk-like appearance.
Most Americans over 45 had the disease as kids. They had endured it with no lasting effects, gained lifelong immunity from reinfection and remember it as a part of childhood, along with measles and chickenpox.
But it's not always so benign, according to Gerberding. While there have been no deaths, at least 20 people in the current outbreak have been hospitalized.
"Up to 10 percent of people will develop meningitis [brain inflammation]," she said. "A certain proportion of people will develop orchitis," an inflammation of the testicles in adolescent boys or adults that can lead to infertility. Other serious but rare complications include spontaneous abortions and deafness.
A long-lasting mumps vaccine has been available since 1967, and some question whether the current outbreak might signal a vaccine failure.
Gerberding said CDC investigators will learn more about the vaccine's effectiveness as they sort through this outbreak. But, she said, "We have absolutely no information to suggest that there is any problem with the vaccine."
Instead, epidemiologists suspect a confluence of several factors.
Increasingly widespread vaccinations since the 1950s have gradually reduced the incidence of mumps in Maryland and across the United States, according to the CDC. From a high of more than 180 cases per 100,000 population in the 1930s, the rate fell to about 40 cases per 100,000 in 1967, when the live virus vaccine was first licensed.