Pneumonia - Hospital-Acquired Disease Background

Introduction

Hospital-acquired pneumonia (HAP) is also known as nosocomial pneumonia. It is defined as pneumonia occurring ≥48 hours after admission and excluding any infection that is incubating at the time of admission. Ventilator-associated pneumonia (VAP) is described as pneumonia occurring >48-72 hours after endotracheal intubation and within 48 hours after the removal of endotracheal (ET) tube.  

Multidrug-resistant (MDR) is defined as an acquired non-susceptibility to at least one agent in three different antimicrobial classes. Extensively drug resistant (XDR) refers to non-susceptibility to at least one agent in all but two antimicrobial classes. Pandrug resistant (PDR) refers to non-susceptibility to all antimicrobial agents that can be used for treatment.  

Epidemiology

Hospital-acquired pneumonia is one of the most common causes of nosocomial infection in hospitalized and intensive care patients. HAP is more common in the elderly; however, the mean age of patients with early-onset HAP is lower than that of patients with late-onset HAP.  

Asian epidemiologic data on hospital-acquired pneumonia are scarce but various health care facilities reported incidences ranging from 1 to 21 per 1000 hospital admissions. 

Pathophysiology

Hospital-acquired pneumonia develops from an imbalance of the normal host defenses and the ability of the microorganism to colonize and invade the lower respiratory tract. Aerobic gram-negative pathogen may cause destructive effects on the lung tissue such as cavitation, microabscess formation, blood vessel invasion and hemorrhage. 

Risk Factors

Risk Factors for Hospital-acquired Pneumonia (HAP)/Ventilator-associated Pneumonia (VAP)

• Patient-related: Age, chronic pulmonary disease, multiple organ system failure, depressed consciousness
• Treatment-related: Intubation/mechanical ventilation, reintubation, prolonged intubation, previous exposure to antibiotics, thoracoabdominal surgery
• Triggers of aspiration: Positioning, nasogastric tube insertion, enteral feeding, low ET tube pressure
• Oropharyngeal colonization

Risk Factors for Multidrug-resistant (MDR) Pathogens

• ≥5 days duration stay for the current hospitalization prior to occurrence of VAP
• Septic shock at the time of HAP/VAP
• ARDS preceding VAP
• Acute renal replacement therapy before VAP onset
• IV antibiotics within the preceding 90 days (risk factor for MDR, Methicillin-resistant Staphylococcus aureus (MRSA), and MDR Pseudomonas VAP and HAP)
• Intensive care unit (ICU) admission
• Structural lung disease (eg bronchiectasis, cystic fibrosis) for HAP
• Colonization with or prior isolation of MDR Pseudomonas or other Gram-negative bacilli