[Epidemiology and mechanisms of pneumonia in adults].

Pneumonia is a major cause of morbidity and mortality in France. Microbial epidemiology, profile of bacterial resistance and prognosis depend on the type of pneumonia (community acquired pneumonia [CAP], health-care associated pneumonia, hospital acquired pneumonia or ventilator associated bacterial pneumonia). Streptococcus pneumoniae, community respiratory viruses, Mycoplasma pneumoniae, Chlamydia pneumonia and Legionella sp. are the five most common pathogens causing CAP in adults. The susceptibility of these four bacteria to antibiotics used in the management of CAP remains stable over time. Comorbidities, risk factors or impairment of the host defence mechanisms changes the microbial classic epidemiology of CAP. Patients with health care-associated pneumonia have an increased risk of multidrug-resistant bacteria, initial inappropriate antimicrobial treatment, severity and mortality, due to a different microbial epidemiology from those of CAP.