Hospital-Acquired Pneumonia Diagnostic Criteria
Hospital-acquired pneumonia (HAP) is diagnosed when pneumonia develops ≥48 hours after hospital admission in non-intubated patients, based on new or progressive radiographic infiltrates plus clinical signs including fever >38.3°C, leukocytosis or leukopenia, and purulent secretions. 1, 2
Clinical Diagnostic Criteria
The diagnosis requires radiological evidence combined with specific clinical findings 1:
- Radiological component: Two successive chest radiographs showing new or progressive lung infiltrates (or a single radiograph if no underlying heart/lung disease) 1
Plus at least one of the following:
- Body temperature >38.3°C without other identifiable cause 1
- Leukocyte count <4,000/mm³ or >12,000/mm³ 1
Plus at least two of the following:
- Purulent sputum 1
- Cough or dyspnea 1
- Declining oxygenation, increased oxygen requirement, or need for respiratory assistance 1
Timing Classification
- Early-onset HAP: Occurs <5 days after hospital admission 1, 3
- Late-onset HAP: Occurs ≥5 days after hospital admission 1, 3
This temporal distinction is critical because early-onset HAP typically involves methicillin-susceptible Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae, while late-onset HAP more commonly involves multidrug-resistant (MDR) pathogens 1.
Microbiological Confirmation
Obtain lower respiratory tract samples before initiating antibiotics to guide definitive therapy 3. Microbiological confirmation identifies causative organisms in approximately 70% of suspected cases 1. The most common pathogens include:
- Pseudomonas aeruginosa 1, 4
- Staphylococcus aureus (including MRSA) 1, 4
- Enterobacteriaceae 1, 4
- Acinetobacter baumannii 1
Polymicrobial infection occurs in 30% of cases 1.
Empiric Antibiotic Regimen for HAP
Risk Stratification Algorithm
The choice of empiric therapy depends on three key factors: mortality risk, MRSA risk factors, and MDR pathogen risk factors. 1, 2, 5
Low Mortality Risk + No MRSA Risk Factors
Use monotherapy with one of the following antipseudomonal beta-lactams 1, 5:
- Piperacillin-tazobactam 4.5 g IV every 6 hours 5
- Cefepime 2 g IV every 8 hours 1, 5
- Meropenem 1 g IV every 8 hours 5
- Imipenem 500 mg IV every 6 hours 5
- Levofloxacin (alternative) 1
Low Mortality Risk + MRSA Risk Factors Present
Add MRSA coverage to the above beta-lactam monotherapy 1, 2, 5:
MRSA risk factors include: hospitalization in units where >20% of S. aureus isolates are methicillin-resistant, or MRSA prevalence is unknown 2.
High Mortality Risk OR Recent IV Antibiotics (Within 90 Days)
Use dual antipseudomonal coverage PLUS MRSA coverage 1, 2:
Dual antipseudomonal options (choose one combination) 2:
- Piperacillin-tazobactam 4.5 g IV every 6 hours PLUS tobramycin or amikacin 2
- Ceftazidime 2 g IV every 8 hours PLUS ciprofloxacin 400 mg IV every 8 hours 2
- Meropenem 1-2 g IV every 8 hours PLUS tobramycin or amikacin 2
PLUS MRSA coverage:
High mortality risk indicators include: septic shock, need for ventilatory support due to HAP, hospitalization >5 days, structural lung disease (bronchiectasis, cystic fibrosis), or prior colonization with MDR pathogens 2.
Early-Onset HAP Without Risk Factors
For patients with early-onset HAP (<5 days), no septic shock, no recent antibiotics, and low institutional resistance rates (<25% MDR pathogens), narrow-spectrum therapy is appropriate 1, 3:
Critical Pitfalls to Avoid
- Never use aminoglycosides as the sole antipseudomonal agent—always combine with a beta-lactam 1, 2
- Never use monotherapy in high-risk patients with prior IV antibiotic exposure within 90 days, as this leads to treatment failure and resistance emergence 2
- Never omit MRSA coverage in patients with prior antibiotic exposure or high institutional MRSA prevalence 2
- Never delay antibiotic administration, as delays are associated with increased mortality 5, 3
Definitive Therapy and De-escalation
Tailor antibiotics based on culture results and clinical response by day 3 2, 3. For uncomplicated HAP with good clinical response, treat for 7-8 days rather than prolonged courses 2. When cultures identify specific pathogens: