A recent study of schoolchildren finds that the youngest students harbor the most germs. Researchers looked at nasal swabs and symptom reports of more than 800 students and staff in Kansas City, Missouri. Kids in pre-kindergarten and elementary school had the highest rates of virus detection compared with older students and staff. The pre-K kids, ages 3 to 5, had the highest rates of actual illness, too. Young children can have up to 10 respiratory viruses as their immune systems are introduced to different infections for the first time. Those viruses include colds, flu and more.