Respiratory tract infections (RTIs) are any infection of the sinuses, throat, airways or lungs.
They're usually caused by viruses, but they can also be caused by bacteria. Respiratory tract infections are believed to be one of the main reasons why people visit their GP or pharmacist. The most widespread respiratory tract infection is the common cold.
Health professionals generally make a distinction between: infections of the upper respiratory tract, which affect the nose, sinuses and throat infections of the lower respiratory tract, which affect the airways and lungs Children tend to get more upper RTIs than adults because they have not yet built up immunity (resistance) to the many viruses that can cause these infections.