Hospital-acquired pneumonia

Last revised by Dr Daniel J Bell on 24 Jun 2020

Hospital-acquired pneumonia (HAP), also known as nosocomial pneumonia, is defined by the American Thoracic Society guidelines as pneumonias that occur more than 48 hours after hospital administration but were not present at the time of admission.

It may be a common cause of pneumonia in patients admitted to intensive care units (ICU) and those on mechanical ventilation. Indeed it is thought that ventilator-associated pneumonia is the commonest type of hospital acquired pneumonia 5. While all ages and both sexes can be affected, elderly patients are more prone to develop it.

Hospital acquired pneumonia is divided into:

  • early onset: within 4 days of admission
  • late onset: after day 5 of admission

Hospital acquired pneumonia commonly results from colonized upper respiratory tract infections being aspirated into the lower respiratory tract and ascending infection from the stomach (i.e. ingested oropharyngeal secretions).

Common organisms for early onset type are Streptococcus pneumoniae and Haemophilus influenzae.

For late onset type, Staphylococcus aureus, Pseudomonas aeruginosaKlebsiella species and Acinetobacter are common.

Intubation and ventilatory support bypass normal defense mechanism predisposing patients to infection.

It is a clinical diagnosis with the imaging features of pneumonia, with no specific findings.

Areas of unilateral or bilateral consolidation may be seen depending on severity. 

The early onset type has a better prognosis. High morbidity and mortality are seen in patients with hospital-acquired pneumonias as they are already hospitalized for another condition. 

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