(Undated) -- A recent surge in cases of a common respiratory virus is raising concerns in Illinois. State health leaders say 11 cases of enterovirus D-68 have been confirmed in the Chicago area. It causes upper respiratory illness and mild symptoms such as low-grade fever, cough, runny nose, and body aches. Melaney Arnold with the Illinois Department of Health says this is the time of year when enterovirus typically circulates and there are about 100 different strains. The Illinois Health Department is working with local health departments and health care providers to monitor for cases of enterovirus D-68 and the C-D-C is assisting with testing. This month, the virus has been linked to hospitalization of hundreds of children in the Midwest.