Respiratory infection: the disease.

Infectious pneumonias are inflammations of the lung that can be localized in the alveoli or interstitial tissue or both. The pathogenic agent is usually airborne; more rarely it is hematogenous. Important distinctions are between bacterial and nonbacterial forms, between diseases acquired outside and inside hospitals, and between patients who are basically healthy and those with a previous illness. Pneumococci continue to be the dominant pathogens outside hospitals. In hospitals, gram-negative, anaerobic, and fungal pathogens are more often found. Usually, purulent chronic bronchitis or an acute exacerbation of chronic bronchitis is based on a prior viral infection or an impairment of bacterial clearance mechanisms of the respiratory tract. The dominant pathogens are Haemophilus influenzae and pneumococci. Worldwide, viral infections of the upper respiratory tract have great epidemiological significance. With 12 different groups of viruses and more than 150 serotypes, there can be many causes of symptoms of rhinitis, tonsillitis, pharyngitis, laryngitis, and tracheitis as well as bronchitis.