WAUSAU, Wis. (AP) -- State health officials say the death of a 12-year-old Wausau area girl, the fourth person to die of swine flu in Wisconsin, continues a pattern of the virus sickening more youths than adults.

Seth Boffeli of the Department of Health and Family Services says of the nearly 3,500 confirmed or probable swine flu cases, 74% are people under the age of 19.

He says the more traditional flu generally hits elderly people the hardest, causing them to see a doctor more than younger people.

Marathon County Health Officer Julie Willems Van Dijk says it's unknown why the number of young people with swine flu is so much higher.

She says researchers are investigating whether older people who were exposed to swine flu in the 1970s may have some protections that young people don't.