SPRINGFIELD -- Public health officials are investigating a sharp increase in the number of mumps cases recorded in central Illinois.
There have been 52 cases of the viral infection reported in Morgan and Sangamon counties so far this year, according to a report in the (Springfield) State Journal-Register.
Across the state, there have been 65 cases reported, including other cases in Fulton, Greene, Champaign, Cook and Will counties. There were 26 cases reported across Illinois in all of 2013.
"This spike is unusual for us," said Jim Stone, director of the Sangamon County Department of Public Health. "It's definitely more than what we would see in the course of a regular year."
The reported cases are mostly in adults between 25 and 53.
Mumps can cause swelling of the salivary glands, along with fever, headaches, muscle aches, tiredness and loss of appetite.
The virus typically isn't fatal, but can cause complications. It's typically spread by droplets of saliva or mucus when someone sneezes or coughs.
Sangamon County health officials say they're working with Southern Illinois University School of Medicine and other physicians to study the increase, but aren't sure what's behind the unusual numbers.
"It may be that we never know why we are seeing this spike," Stone said.