Acute Infectious Pneumonia
Anna G. Rudnicki
Andres F. Sosa
I. GENERAL PRINCIPLES: Pneumonia in the immunocompetent patient.
A. Pneumonia in the intensive care unit (ICU).
1. Severe community-acquired pneumonia (CAP).
a. Criteria have been proposed by the Infectious Disease Society of America and the American Thoracic Society (Table 56-1).
b. Mortality rates for patients admitted to the ICU with CAP range from 21% to 54%.
c. Early and effective empiric therapy and ICU admission improve survival (Table 56-2).
d. Underlying comorbidity and certain medical interventions increase the risk for pneumonia and increase morbidity and mortality.
2. Nosocomial pneumonia: hospital-acquired pneumonia (HAP), occurs 48 hours after admission and was not incubating before arrival to the hospital, and ventilator-associated pneumonia (VAP), pneumonia developing after 48 to 72 hours of intubation. Health care-associated pneumonia (HCAP): Criteria include hospitalization for 2 or more days within the past 90 days, resident of nursing home or long-term acute care, receiving hemodialysis, intravenous therapy, or home wound care.
a. The infection most likely to contribute to death of hospitalized patients.
b. Risk factors for nosocomial pneumonia.
i. Underlying acute illness: predisposes to secondary pneumonia.
ii. Coexisting medical illness.
iii. Malnutrition.
iv. Other risks: general surgery, acute respiratory distress syndrome (ARDS), head injury, advanced age, obesity, cardiopulmonary disease, renal failure, malignancy, diabetes mellitus, endotracheal intubation, mechanical ventilation (VAP), tracheostomy, nasogastric tube, and use of corticosteroids, antibiotics, or H2 antagonists.
c. Additional risk factors for VAP: intubation and mechanical ventilation (risk is 3%/day first 5 days, 2%/day 5 to 10 days, and 1%/day after 10 days), reintubation, nasotracheal and nasogastric tubes, antibiotic use, colonization with virulent pathogens, aspiration (supine position), and parenteral nutrition.
TABLE 56-1 Criteria for Severe Community-Acquired Pneumonia | ||||||||||||||||||||||||||||||||
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II. PATHOGENESIS: Understanding normal host defenses (e.g., humoral immunity, cough) and their potential impairments is valuable in assessing those at risk for pneumonia in general and select pathogens in specific (e.g., Pneumocystis jiroveci with impaired cellular immunity). A more thorough discussion of this topic is referenced.
III. ETIOLOGY
A. Severe CAP.
1. Organism causing pneumonia identified in approximately 50%.
2. Most common organisms leading to ICU admission for CAP: pneumococcus, Legionella pneumophila, epidemic viruses (influenza), Staphylococcus aureus (including MRSA), and enteric gram-negative bacilli.
3. In specific clinical settings, certain pathogens may be more common (e.g., injection drug use, S. aureus; neutropenia, Pseudomonas aeruginosa).
B. Nosocomial pneumonia.
1. Early-onset HAP occurs within the first 4 days of hospitalization; likely pathogens are similar to CAP.
2. Late-onset HAP occurs 5 days or more from hospital admission, HCAP, and VAP caused by a variety of gram-positive and gram-negative bacteria, many of which are multidrug resistant (MDR).
3. More common organisms: gram-negative bacilli such as P. aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter.
TABLE 56-2 Empiric Therapy for Nosocomial Pneumonia Requiring ICU Admission | ||||||
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