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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.
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PMID:Changes in the spectrum of organisms causing respiratory tract infections: a review. 128 13

This document updates and replaces CDC's previously published "Guideline for Prevention of Nosocomial Pneumonia" (Infect Control 1982;3:327-33, Respir Care 1983;28:221-32, and Am J Infect Control 1983;11:230-44). This revised guideline is designed to reduce the incidence of nosocomial pneumonia and is intended for use by personnel who are responsible for surveillance and control of infections in acute-care hospitals; the information may not be applicable in long-term-care facilities because of the unique characteristics of such settings. This revised guideline addresses common problems encountered by infection-control practitioners regarding the prevention and control of nosocomial pneumonia in U.S. hospitals. Sections on the prevention of bacterial pneumonia in mechanically ventilated and/or critically ill patients, care of respiratory-therapy devices, prevention of cross-contamination, and prevention of viral lower respiratory tract infections (e.g., respiratory syncytial virus [RSV] and influenza infections) have been expanded and updated. New sections on Legionnaires disease and pneumonia caused by Aspergillus sp. have been included. Lower respiratory tract infection caused by Mycobacterium tuberculosis is not addressed in this document. Part I, "An Overview of the Prevention of Nosocomial Pneumonia, 1994, provides the background information for the consensus recommendations of the Hospital Infection Control Practices Advisory Committee (HICPAC) in Part II, Recommendations for Prevention of Nosocomial Pneumonia." Pneumonia is the second most common nosocomial infection in the United States and is associated with substantial morbidity and mortality. Most patients who have nosocomial pneumonia are infants, young children, and persons > 65 years of age; persons who have severe underlying disease, immunosuppression, depressed sensorium, and/or cardiopulmonary disease and persons who have had thoracoabdominal surgery. Although patients receiving mechanically assisted ventilation do not represent a major proportion of patients who have nosocomial pneumonia, they are at highest risk for acquiring the infection. Most bacterial nosocomial pneumonias occur by aspiration of bacteria colonizing the oropharynx or upper gastrointestinal tract of the patient. Because intubation and mechanical ventilation alter first-line patient defenses, they greatly increase the risk for nosocomial bacterial pneumonia. Pneumonias caused by Legionella sp., Aspergillus sp., and influenza virus are often caused by inhalation of contaminated aerosols. RSV infection usually occurs after viral inoculation of the conjunctivae or nasal mucosa by contaminated hands. Traditional preventive measures for nosocomial pneumonia include decreasing aspiration by the patient, preventing cross-contamination or colonization via hands of personnel, appropriate disinfection or sterilization of respiratory-therapy devices, use of available vaccines to protect against particular infections, and education of hospital staff and patients. New measures being investigated involve reducing oropharyngeal and gastric colonization by pathogenic microorganisms.
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PMID:Guidelines for prevention of nosocomial pneumonia. Centers for Disease Control and Prevention. 903 4

Pneumonia is the second most common nosocomial infection in the United States and is associated with substantial morbidity and mortality. Most patients with nosocomial pneumonia are those with extremes of age, severe underlying disease, immunosuppression, depressed sensorium, and cardiopulmonary disease, and those who have had thoracoabdominal surgery. Although patients with mechanically assisted ventilation do not comprise a major proportion of patients with nosocomial pneumonia, they have the highest risk of developing the infection. Most bacterial nosocomial pneumonias occur by aspiration of bacteria colonizing the oropharynx or upper gastrointestinal tract of the patient. Intubation and mechanical ventilation greatly increase the risk of nosocomial bacterial pneumonia because they alter first-line patient defenses. Pneumonias due to Legionella spp., Aspergillus spp., and influenza virus are often caused by inhalation of contaminated aerosols. Respiratory syncytial virus (RSV) infection usually follows viral inoculation of the conjunctivae or nasal mucosa by contaminated hands. Traditional preventive measures for nosocomial pneumonia include decreasing aspiration by the patient, preventing cross-contamination or colonization via hands of personnel, appropriate disinfection or sterilization or respiratory therapy devices, use of available vaccines to protect against particular infections, and education of hospital staff and patients. New measures under investigation involve reducing oropharyngeal and gastric colonization by pathogenic microorganisms.
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PMID:Guideline for prevention of nosocomial pneumonia. Centers for Disease Control and Prevention. 1014 36

Community-acquired pneumonias (CAP) are still caused by Streptococcus pneumoniae, Hemophilus influenzae, or Moraxella catarrhalis. Legionella and Chlamydia pneumoniae have been defined as important atypical pathogens causing CAP. Klebsiella causes CAP primarily in patients with chronic alcoholism or in chronic care facilities. Normal hosts do not present with "unusual pathogens'' e.g., Staphylococcus aureus or Pseudomonas aeruginosa. The clinical severity of a bacterial pneumonia has important prognostic implications and predicts admission to intensive care units, duration of therapy, and complications. The factors that determine the severity of a CAP are less related to the pathogen than the underlying cardiopulmonary status of the patient as well as the patient's humoral immunity. Relatively avirulent pathogens may result in severe CAP in patients with diminished/absent splenic function or significant cardiopulmonary disease. A critical concept is to appreciate that the selection of antimicrobial therapy is not dependent on co-morbidities since the antimicrobial therapy is directed against the pathogen and not the co-morbidities. Therefore the treatment of CAP, whether moderate or severe is with the same antibiotic at the same dose. Many antibiotic regimens are equally efficacious in the treatment of CAP. The most cost effective optimal regimen covers both typical and atypical pathogens, e.g., levofloxacin, and is currently the preferred antibiotic approach to moderate or severe CAP in the CCU.
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PMID:The antibiotic treatment of severe community-acquired pneumonia admitted to the critical care unit. 1608 19