While COVID-19 cases among young people continue to rise, doctors are also warning parents about another serious health threat for children.There has been a sudden spike in cases of a severe respiratory illness in infants — respiratory syncytial virus, or RSV."It's called RSV bronchiolitis and it can cause terrible difficulty breathing, wheezing, runny nose, fevers and unfortunately, a good number of infants get hospitalized," Aurora Children's Health Medical Director Dr. Kevin Dahlman said.The potentially severe respiratory illness typically occurs in the fall and winter months.Symptoms are often mild, but Dahlman said it was hitting earlier and harder this year than before. There has been a 400% jump in cases from July to August.Dahlman said Aurora Children's was also seeing a four-fold increase in hospitalizations.The younger the child, he said, the more serious the threat.The risk is particularly great for children born prematurely and those who end up hospitalized and on oxygen.Dahlman said there were also long-term effects that can result from RSV."That can certainly cause some short and long-term lung damage," he said.Damage could also include asthma. He urged parents to watch for any signs of breathing difficulties in their infants."If your child looks like they're in distress, no matter what the underlying cause may be, seek help immediately," Dahlman said.He added that it was unclear whether the earlier-than-usual spike in RSV cases will lead to a bigger surge in the fall and winter.