Upper Respiratory Infections Upper respiratory tract includes nose, nostrils, nasal cavity, mouth, oral cavity, pharynx and larynx. Virus and bacteria enter upper respiratory tract causing an infection. Most common URI-causing viruses are rhinovirus, influenza virus, adenovirus, enterovirus and respiratory synctial virus. An infected individual can transmit these viruses by expelling respiratory droplets when coughing, sneezing and even coughing. URI mainly manifests with coughing, sneezing, fever, headache, irritability, painful swallowing, and wheezing.