Common cold virus. Computer artwork of a rhinovirus particle, the most important cause of the common cold and upper respiratory tract infections. Rhinoviruses belong to the Picornaviridae family which comprises small (about 30 nanometres in diameter) RNA viruses with a naked (without external envelope) capsid structure. Rhinoviruses are spread readily in air by droplets produced by coughing and sneezing. The clinical symptoms of infections caused by rhinoviruses include sneezing, nasal obstruction, mild sore throat and headache.