Registered Nurse Judy Walker holds a dose of the swine flu vaccine nasal mist at Children's Memorial Hospital in Chicago on Monday, Oct. 5, 2009. Children's Memorial Hospital received 500 doses of the vaccine to inoculate people against the virus, which has been blamed for hundreds of deaths since it was first identified in April. (AP Photo/David Banks)
The death of Michelle Lahle, 14, would be the first associated with swine flu in the county.
The full investigation is likely to take 10 to 14 days.
"This is a tragic reminder for parents, teachers, students and members of the community to really try to prevent illness," said Dr. Rashmi Chugh, medical officer at the DuPage County Health Department.
As school officials waited for the cause of death, some parents who arrived for parent-teacher conferences said the uncertainty convinced them to have their children vaccinated for swine flu.