organisms causing respiratory tract infection
Read our leaflet about Antibiotics: Why some people need them and some don't. Respiratory tract infections (RTIs) can be caused by viruses, bacteria and (less often) fungi. Most common respiratory tract infections such as colds, sore throats, sinusitis and laryngitis are caused by viruses.One type of virus can cause more than one type of RTI. For example, the viruses that cause a cold can also cause: 1  sinus infections (sinusitis).acteria can also cause RTIs, including serious infections such as pneumonia and whooping cough (pertussis) . Sometimes bacteria can cause a second infection after you have had an RTI caused by a virus. Find out more about different respiratory tract infections.