U.S. government health officials said Wednesday that an outbreak of mumps has hit states in the U.S. Midwest and shows no signs of ending. More than 1,100 cases of the contagious disease have occurred during the past four months.

The Centers for Disease Control and Prevention (CDC) says that, on average, only about 250 cases of mumps occur in the United States every year. The current outbreak was first detected in the state of Iowa, in the central United States, in December.

CDC Director Dr. Julie Gerberding says the mumps outbreak has spread from Iowa to seven other states and other possible cases are under investigation. "There are 815 reported cases in Iowa, at least as of our last communication with the Iowa state Health Department, so that by far is the largest number of cases that we're aware of so far. There are 350 cases reported from seven other states, which include Minnesota, Kansas, Illinois, Nebraska, Wisconsin, Missouri and Oklahoma," she said.

Infants in the United States have been routinely vaccinated against the mumps virus since a vaccine was developed in the 1960s. Most of the cases in the current outbreak have occurred among people 18 to 25 years of age who had been vaccinated.

Mumps is a virus spread by coughing and sneezing. The most common symptoms are fever, headache and swollen salivary glands under the jaw. But it can lead to more severe problems, such as hearing loss and meningitis.

Dr. Gerberding said the U.S. outbreak may be connected to an outbreak of more than 100,000 cases in the United Kingdom during the past two years. "We do know that the genotype, at least in the early cases of this outbreak, was the same genotype of virus that was associated with the United Kingdom outbreak. But that doesn't necessarily mean there was a direct link to introduction. (It is) certainly possible, but we don't have any proof of that at this point in time," she said.

Vaccine is being shipped to Iowa in an attempt to reduce the spread of the disease. In the current outbreak, only about 20 people have been hospitalized and no one has died.