Nosocomial Respiratory Infections

Published on 12/06/2015 by admin

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Chapter 27 Nosocomial Respiratory Infections

Epidemiology

Pathogenesis

Sources of Colonization

Etiologic Agents

Nosocomial respiratory infections may be caused by a variety of pathogens, and often more than one pathogen may be isolated. Microorganisms responsible for those infections differ according to the studied population, the duration of hospital stay, and the specific diagnostic methods used. Nosocomial respiratory infections are commonly caused by aerobic, gram-negative bacilli, such as P. aeruginosa, Escherichia coli, Klebsiella pneumoniae, or Acinetobacter spp., whereas Streptococcus aureus is the predominant isolated gram-positive pathogen. In a recent report by Esperatti and colleagues, the etiology of nosocomial pneumonia was investigated for invasively versus noninvasively ventilated patients managed in the ICU. Of interest, no significant differences were found, except for a higher proportion of S. pneumoniae in the noninvasively ventilated patients. These results imply that prevalence rates for nosocomial pathogens are similar in intubated and nonintubated patients, and that the use of empirical therapy likely to be active against them is warranted.

Underlying diseases may predispose patients to infection with specific organisms. For instance, patients with chronic obstructive pulmonary disease (COPD) are at increased risk for Haemophilus influenzae, Moraxella catarrhalis, P. aeruginosa, or S. pneumoniae infections; patients with acute respiratory distress syndrome (ARDS) are at higher risk for development of VAP caused by S. aureus, P. aeruginosa, and Acinetobacter baumannii. Finally, patients with traumatic injuries and neurologic disorders are at increased risk for S. aureus, Haemophilus, and S. pneumoniae infections.

Identification of pathogens resistant to multiple drugs is extremely important, in order to guide appropriate antibiotic treatment. Potential MDR pathogens are P. aeruginosa, MRSA, Acinetobacter spp., Stenotrophomonas maltophilia, Burkholderia cepacia, and extended-spectrum beta-lactamase–producing (ESBL-positive) K. pneumoniae. Conversely, S. pneumoniae, H. influenzae, methicillin-sensitive S. aureus, and antibiotic-sensitive Enterobacteriaceae organisms are not considered to be MDR pathogens. The incidence of MDR pathogens is closely linked to local factors and varies widely from one hospital to another. Accordingly, practitioners must be aware of the most prevalent microorganisms in their own clinical facilities and geographic regions to avoid the administration of initial inadequate antimicrobial therapy.

Legionella pneumophila as a cause of nosocomial pneumonia should be considered, particularly in immunocompromised patients. Anaerobes may potentially cause nosocomial infections, but often those pathogens are identified in association with aerobic pathogens, and their role is still considered controversial. Nosocomial infections are rarely caused by a fungus. Candida spp. and Aspergillus fumigatus are the most common isolated fungi, predominantly in immunocompromised patients. Finally, herpes simplex virus type 1 and cytomegalovirus (CMV) are the most common viruses identified as a cause of respiratory infections in hospitalized patients; of note, CMV pneumonia was found to be consistently associated with worse outcomes in patients managed in the ICU.

Prevention

Nosocomial respiratory infections are associated with high morbidity and mortality and constitute an important burden for the health care system; therefore, appropriate preventive strategies, summarized in Box 27-1, should be implemented to reduce overall incidence of those diseases. Approaches with proven efficacy in reduction of nosocomial respiratory infections should be grouped and implemented as a bundle, because together they are expected to result in a better outcome than when implemented individually.