ABSTRACT
Pneumonia is one of the commonest of the 'nosocomial infections', that is, infections which are acquired by patients as a result of their stay in hospital. The aetiological agents involved in hospital-acquired pneumonia are related to the origin of the infection. Pneumonia in ventilated patients is suspected if there are features such as new infiltrates on the chest radiograph, a drop in arterial P02j changes in pattern of fever, or increased respiratory secretions. The pathogenic organisms which invade the lung in hospitalized patients are often derived from the population of organisms which have colonized the patient's own upper respiratory tract. Cross- infection, from other patients or health care workers, involves viruses such as influenza A or B, adenoviruses, respiratory syncytial virus and SARS coronavirus. Patients on ventilators are particlarly at risk. Infection usually derives from hospital-acquired colonization of the patient's upper respiratory tract with potential pathogens such as methicillin-resistant Staphylococcus aureus, resistant Gram-negative bacilli, or yeasts.
