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.


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.


Aerobic Gram Negative Pathogens

Gram-Positive Pathogens

Elderly Population

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

Ventilator-associated Pneumonia (VAP)

  • The microbiologic flora responsible for VAP is different from that of the more common community-acquired pneumonia (CAP). In particular, viruses and fungi are uncommon causes in people who do not have underlying immune deficiencies.
  • Though any microorganism that causes CAP can cause VAP, there are several bacteria which are particularly important causes of VAP because of their resistance to commonly used antibiotics. These bacteria are referred to as multidrug resistant (MDR).
  • 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. [2]
  • 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).

The following is a list of the most MDR common pathogens associated with ventilator-associated pneumonia:


  1. "Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia". American Journal of Respiratory and Critical Care Medicine. 171 (4): 388–416. 2005. doi:10.1164/rccm.200405-644ST. PMID 15699079. Retrieved 2012-09-12. Unknown parameter |month= ignored (help)

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