The usual causative agents of URTI are viruses including rhinovirus, influenza, parainfluenza, RSV, human metapneumovirus, enterovirus, adenovirus, Ebstein Barr virus and herpes simplex virus.
Non-viral causes include Streptococcus pyogenes, Pneumococcus, Moraxella, H. influenzae, S. aureus, B. pertussis, Mycoplasma, gonorrhoea and C. diphtheriae.