Illinois' mumps outbreak has reached 200 confirmed cases.
Health officials say the virus has infected several people connected with two high schools in the city of Normal.
The (Champaign) News-Gazette reports that the cases are linked to Normal West and University high schools.
The McLean County Health Department is sending letters to students, faculty and staff who have had contact with those infected.
Mumps is no longer common in the U.S. The number of cases ranges from a couple hundred to a couple thousand a year.
The measles, mumps and rubella vaccine prevents most, but not all, cases.
Symptoms include fever, headache, tiredness and swollen salivary glands under the ears.
The state's outbreak has centered on the University of Illinois' Urbana-Champaign campus, where 134 cases have been confirmed.