Infectious Diseases in Critical Care Medicine

11

Nosocomial Pneumonia in Critical Care

Emilio Bouza

Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario ‘‘Gregorio Maran ̃o ́n’’,

Madrid, and CIBER de Enfarmedades Respiratorias (CIBERES), Madrid, Spain

Almudena Burillo

Clinical Microbiology Department, Hospital Universitario de Mo ́stoles, Madrid, Spain

INTRODUCTION
Nosocomial pneumonia or hospital-acquired pneumonia (HAP) is defined as pneumonia that
appears 48 hours or more after hospitalization. In this definition, it is assumed that the patient
was not incubating the causative microorganism when admitted to the hospital. Patients with
HAP may be managed in a ward or, when the illness is severe, in the intensive care unit (ICU).
Most cases of HAP occur outside ICUs. However, patients on mechanical ventilation carry the
highest risk of HAP, and it is in these patients that the entity has been best studied. Ventilator-
associated pneumonia (VAP) refers to pneumonia that begins and develops after endotracheal
intubation (1,2). However, a patient who has just undergone tracheotomy and is not yet on a
ventilator is similarly susceptible to VAP. Thus, a more appropriate term would be
“endotracheal-tube-associated pneumonia.” In this chapter, we have, nevertheless, opted for
the traditional term.

Epidemiology
HAP is currently the second most common nosocomial infection in North America and is
associated with high rates of morbidity and mortality. Although HAP is not a reportable
illness, available data indicate a rate of 5 to 10 cases per 1000 hospital admissions, and this rate
is 6 to 20 times higher in patients subjected to mechanical ventilation (3,4). Nevertheless, the
incidence density of VAP varies widely depending on the case definition of pneumonia and
the hospital population evaluated. Numbers of reported episodes per 1000 days of ventilation
are 34.5 after major heart surgery (5), 26 in a burns ICU (6), 18.7 in a pediatric ICU (7), and
between 8.0 (8) and 46.3 (9) in mixed medical/surgical ICUs. The most recent report by the
Centers for Disease Control National Nosocomial Infection Surveillance (NNIS) System
indicates that surgery and trauma ICUs have the highest VAP rates (mean 15.2/1000 ventilator
days), followed by medical ICUs (mean VAP rate, 4.9); coronary ICUs (mean VAP rate, 4.4);
and surgical ICUs (mean VAP rate, 9.3) (10). Between 10% and 20% of patients receiving

48 hours of mechanical ventilation will develop VAP (11).
The incidence of VAP in mechanically ventilated patients rises as the time of ventilation
lengthens. The incidence of VAP is highest early during the course of a hospital stay, with
estimates of 3% per day during the first five days of ventilation, 2% per day from days 5 to 10,
and 1% per day thereafter (12). Approximately half of all VAP episodes occur within the first
four days of mechanical ventilation. The intubation process itself carries a risk of infection,
such that when acute respiratory failure is noninvasively managed, the rate of nosocomial
pneumonia is lower (13–17).
The overall mortality rate for HAP may be as high as 30% to 70%, but many critically ill
patients with HAP die of their underlying disease rather than of pneumonia. VAP-related
mortality has been estimated at 33% to 50% in several case-matched studies. Critically ill
patients who develop VAP appear twice as likely to die compared with similar patients
without VAP (odds ratio, 2.03; 95% confidence interval (CI), 1.16 to 3.56) (11). Increased
mortality rates have been attributed to the following factors: bacteremia, especially that caused