Respiratory tract infections (RTIs) are any infection which refers to infection of respiratory tract like sinuses, throat, airways or lungs. They're usually caused by viruses, but can also be caused by bacteria. common cold is the most widespread type of (RTIs). Respiratory tract infections are mainly classified into two types. upper respiratory tract infections - airway above the glottis or vocal cords which affect the nose, sinuses and throat. lower respiratory tract infections- The lower respiratory tract consists of the trachea (wind pipe), bronchial tubes, the bronchioles, and the lungs which affect the airways and lungs mainly. Few examples of upper tract Infection are tonsillitis, sinusitis, Flu and common cold. And for Lower tract infection examples are tuberculosis, Bronchitis, pneumonia.