title: Changes in the spectrum of organisms causing respiratory tract infections: a review.
abstract: Over the last decade, the spectrum of organisms causing community-acquired acute lower respiratory tract infections has changed. Streptococcus pneumoniae now causes approximately 30% of outpatient acute pneumonia-less than in former decades-whereas Mycoplasma pneumoniae is found in both young and elderly patients. The Enterobacteriaceae and Staphylococcus aureus are now seen more frequently as respiratory tract pathogens in community-acquired pneumonia patients, and they are the major organisms causing pneumonia in residents of homes for the elderly or nursing homes, and in immuno-compromised patients. Agents that were previously considered non-pathogenic for the respiratory tract include serotypes of Haemophilus influenzae other than type b, H. parainfluenzae and Moraxella (Branhamella) catarrhalis; these organisms affect mainly patients with underlying cardiopulmonary disease. Legionella species can cause sporadic as well as epidemic disease of the lower respiratory tract. Chlamydia pneumoniae is a newly recognized pathogen responsible for mild to severe upper and lower respiratory tract infections. In 60-80% of cases, hospital-acquired pneumonias are caused by Gram-negative bacilli and S. aureus. These organisms colonize the mucosal membranes of the upper respiratory tract and penetrate into the lower tract by aspiration or intubation.
authors.affiliation: Institute of Medical Microbiology, University of Zurich, Switzerland.
authors.forename: F H
authors.initials: FH
authors.lastname: Kayser
mesh_terms: D001991:Bronchitis / Q000382:microbiology; D003428:Cross Infection; D004756:Enterobacteriaceae Infections / Q000382:microbiology; D006192:Haemophilus Infections / Q000382:microbiology; D006801:Humans; D011008:Pneumococcal Infections / Q000382:microbiology; D011014:Pneumonia / Q000382:microbiology; D012141:Respiratory Tract Infections / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000382:microbiology; D013296:Streptococcus pneumoniae