Adenoviruses are medium-sized (90–100 nm), nonenveloped (naked) icosahedral viruses composed of a nucleocapsid and a double-stranded linear DNA genome. There are more than 51 different serotypes in humans, which are responsible for 5–10% of upper respiratory infections in children, and a number of infections in adults as well. Adenoviruses are primarily spread via respiratory droplets. However, they can also be spread by fecal routes as well. Adenovirus infections often show up as tonsilitis, conjunctivitis, an ear infection, or croup.