Nosocomial Pneumonia Definition and Criteria

Definition of Nosocomial Pneumonia

The American Thoracic Society defines nosocomial pneumonia as pneumonia that occurs 48 hours or more after hospital admission and was not incubating at the time of admission 1, 3
For infections that develop after discharge, the same temporal criterion applies: an infection that appears within 48 hours after discharge may be considered nosocomial 2
This definition is consistent with the general incubation period considered for nosocomial infections, which is 48 hours (except for infections with known incubation periods, such as legionellosis) 1

A bacterial strain is presumed to be of nosocomial origin if it is isolated from a patient who has been hospitalized for at least 48 hours or was transferred from another medical care facility 1
Inversely, an infection diagnosed within the first 48 hours after discharge may be linked to a previous hospital stay 2
To determine with precision whether a post-discharge pneumonia is nosocomial, the following must be considered: patient characteristics 1, clinical history 2, and the nature of the infection 2

Essentially nosocomial infections (such as MRSA) may be mistakenly considered community-acquired if there was an unrecorded previous hospital stay 1
Any infection diagnosed within the first 48 hours after readmission may be community-acquired or linked to a previous hospital stay 2
To determine the origin, factors such as the type of pathogen (multidrug-resistant pathogens are often nosocomial) 1 and patient risk factors 1, 2 must be evaluated

Resistance rates are higher among bacteria that cause nosocomial infections than among those that cause community-acquired infections 2
This distinction is crucial for the appropriate selection of antibiotics 4, infection control 2, and epidemiological surveillance 1, 2
Nosocomial pneumonia is associated with mortality rates of 20-50% and attributable mortality rates of 30-33% 4

The Centers for Disease Control and Prevention recommend that factors such as advanced age, endotracheal intubation, mechanical ventilation, depressed level of consciousness, underlying chronic lung disease, and previous episodes of large-volume aspiration be considered as risk factors for nosocomial pneumonia 4