Hospital-acquired pneumonia causes

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Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. ; Philip Marcus, M.D., M.P.H.

Overview

The majority of cases related to various gram-negative bacilli (52%) and S. aureus (19%). Others are Haemophilus spp. (5%). In the ICU results were S. aureus(17.4%), P. aeruginosa (17.4%), Klebsiella pneumoniae and Enterobacter spp. (18.1%), and Haemophilus influenzae (4.9%). Viruses -influenza and respiratory syncytial virus and, in the immunocompromised host, cytomegalovirus- cause 10-20% of infections.

Causes

Aerobic Gram Negative Pathogens

• Commonly polymicrobial
• Common microbial agents include:
  • Pseudomonas aeruginosa
  • Escherichia coli
  • Klebsiella pneumoniae
  • Acinetobacter

Gram-Positive Pathogens

• Staphylococcus aureus
• Methicillin resistant staphylococcus aureus (common in patients with diabetes mellitus, head trauma, and in ICU)

Elderly Population

• S. aureus
• Enteric gram-negative rods
• Streptococcus pneumoniae
• Pseudomonas

Ventilator-associated Pneumonia (VAP)

• VAP has been classified into either early-onset pneumonia (EOP), if pneumonia develops within 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation, and late-onset pneumonia (LOP), if pneumonia develops after 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation.
• This categorization can be helpful to clinicians in initiating empiric antimicrobial therapy for cases of pneumonia, when the results of microbiologic diagnostic testing are not yet available.
• EOP has been associated usually with non-multi-antimicrobial-resistant microorganisms such as Escherichia coli, Klebsiella spp., Proteus spp., S. pneumoniae, H. influenzae, and oxacillin-sensitive S. aureus.
• On the other hand, LOP has been associated with Pseudomonas aeruginosa, oxacillin-resistant S. aureus, and Acinetobacter spp-- strains that are usually multi-antibiotic-resistant.