Any infectious disease affecting the respiratory system.

Upper respiratory tract infections (URTIs) include the common cold, laryngitis, pharyngitis/tonsillitis, rhinitis, rhinosinusitis and acute otitis media. URTIs are mostly viral infections and do not require antibiotic treatment. They are largely self-limiting, and complications are likely to be rare. Antibiotics are not usually needed although often prescribed.

Lower respiratory tract infections (LRTIs) include acute bronchitis, bronchiolitis, pneumonia and tracheitis. They are generally more serious, particularly in children and older people. They can be caused by a range of bacterial pathogens and can require antibiotic treatment.

RTIs are a major cause of mortality globally and one of the most frequent triggers of antibiotic use. Overuse of antibiotics for RTIs is a driver of antibiotic resistance.

RTIs are among the most important hospital-acquired infections (HAIs), many of which are caused by drug-resistant strains of bacteria. Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) have particularly high mortality rates.