Flu season is in high gear, but other viruses can cause similar symptoms.

“If you have upper respiratory symptoms, it’s going to be almost impossible for anybody to distinguish between adenovirus and influenza without doing further testing,” says Amesh Adalja, MD, an infectious disease physician and senior scholar at Johns Hopkins University Center for Health Security in Baltimore.

While adenoviruses may be less known than the flu, they are very common among young people. Most children have had at least one adenovirus infection by age 10.

Adenovirus infections are typically mild and do not pose the same health threat as influenza. During the last flu season, more than 80,000 people died from influenza-related complications.