Lucan · Conditions

Hospital-acquired pneumonia

Australian guidance: eTG Antibiotic — HAP/VAP

1. Definition and epidemiology

Hospital-acquired pneumonia (HAP) is pneumonia developing at least 48 hours after hospital admission in a patient who was not intubated at the time of diagnosis. Ventilator-associated pneumonia (VAP) is a distinct subcategory arising more than 48 hours after endotracheal intubation and is managed under a separate eTG pathway. HAP is the second most common healthcare-associated infection in Australian hospitals and carries a crude mortality of 20 to 30 percent, with attributable mortality of around 5 to 10 percent after adjusting for underlying illness severity. Incidence in Australian acute care settings is estimated at 5 to 10 episodes per 1000 hospital admissions, with higher rates in intensive care units and surgical wards.

2. Pathophysiology

HAP arises through one of two dominant routes: micro-aspiration of colonised oropharyngeal secretions into the lower airways, or haematogenous seeding from a distant source. In hospitalised patients, the normal oropharyngeal flora shifts within 48 to 72 hours toward gram-negative enteric bacilli (Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii) and Staphylococcus aureus, including methicillin-resistant strains (MRSA). Impaired mucociliary clearance from intubation, sedation, and supine positioning allows colonising organisms to reach the alveoli unchallenged. Robbins (Ch 15) describes the subsequent sequence: organisms overwhelm alveolar macrophage defences, triggering neutrophil recruitment and fibrinous exudate filling alveolar spaces. In gram-negative HAP, lipopolysaccharide-driven cytokine release amplifies the inflammatory cascade, causing consolidation and, in severe cases, parenchymal necrosis. Coagulase-negative staphylococci and oral streptococci that predominate in community pneumonia are correspondingly rare in HAP beyond the first 48 hours of admission.

3. Clinical presentation and diagnostic criteria

HAP presents with the new appearance of fever (temperature above 38.3 degrees Celsius), purulent sputum or increased secretions, leucocytosis or leucopenia, and a new or progressive infiltrate on chest imaging, all occurring at least 48 hours into admission. The clinical diagnosis requires at least two of the three signs (fever, leucocytosis or leucopenia, purulent secretions) plus a new radiological infiltrate. On examination there is dullness to percussion, bronchial breath sounds, and increased tactile fremitus over the affected lobe. Hypoxia with a fall in SpO2 or PaO2 to FiO2 ratio below 300 mmHg suggests moderate to severe disease. The CPIS (Clinical Pulmonary Infection Score) is a six-variable bedside score that has been used in research settings, but eTG does not mandate its routine use; clinical judgement plus the criteria above remains the standard AU approach. Late-onset HAP (beyond 96 hours of admission) carries a higher probability of resistant organisms and informs empirical antibiotic selection.

4. Investigations and AU-specific cutoffs

Investigations should be collected before commencing antibiotics where clinically safe to do so, consistent with ACSQHC Quality Statement 4.

• Sputum or endotracheal aspirate for microscopy, culture, and sensitivity (MC+S): the key microbiological sample; a semiquantitative culture threshold of 10^6 colony-forming units per millilitre in endotracheal aspirate supports VAP diagnosis but is not applied to standard HAP sputum specimens.
• Blood cultures: two sets from separate sites; positive in only 10 to 15 percent of HAP episodes but guide de-escalation.
• Full blood count: leucocytosis above 11 x 10^9/L or leucopenia below 4 x 10^9/L supports infection.
• C-reactive protein and procalcitonin: procalcitonin is useful for guiding duration of therapy (target to fall 80 percent from peak or below 0.25 micrograms per litre to guide cessation); not a diagnostic cutoff for HAP.
• Chest X-ray (AP): new lobar or segmental consolidation. CT chest is not routinely required but clarifies complex or atypical appearances.
• Arterial blood gas or pulse oximetry: SpO2 below 94 percent on room air is the AU threshold for supplemental oxygen initiation in most adults.
• Urea, creatinine, and electrolytes: monitor renal function before and during aminoglycoside or vancomycin use.
• Nasopharyngeal swab for respiratory viruses (influenza PCR): indicated in outbreaks or influenza season.

Avoid delaying empirical antibiotics beyond one hour in the presence of septic shock (ACSQHC Quality Statement 1).

5. Management

Management follows the eTG Antibiotic HAP/VAP pathway and is stratified by disease severity and risk factors for resistant organisms.

Non-severe HAP, low risk of resistant organisms (early-onset, no prior broad-spectrum antibiotics, no known MRSA colonisation): Oral or intravenous amoxicillin plus clavulanate (875 mg/125 mg orally every 12 hours, or 1.2 g IV every 8 hours) for 5 to 7 days. Alternatively, IV cefazolin 2 g every 8 hours is an option when gram-negative cover is the primary concern and the patient cannot take oral therapy.

Moderate to severe HAP, or risk factors for resistant gram-negative organisms (late-onset, prior broad-spectrum antibiotics, structural lung disease, immunocompromise): IV piperacillin/tazobactam 4.5 g every 6 hours (extended infusion over 4 hours preferred for pharmacodynamic optimisation) is the eTG preferred agent. For documented or likely Pseudomonas aeruginosa risk, IV cefepime 2 g every 8 hours or IV meropenem 1 g every 8 hours are alternatives based on local antibiogram data.

MRSA risk (prior MRSA colonisation, prolonged prior vancomycin use, ICU admission, skin breach): Add IV vancomycin with target trough-guided or AUC-guided dosing; AUC/MIC target of 400 to 600 mg.h/L is the current AU standard. Linezolid 600 mg IV/oral every 12 hours is the alternative when renal toxicity is a concern.

Duration: 5 to 7 days for most HAP episodes once there is clinical improvement, consistent with antimicrobial stewardship principles. De-escalate to the narrowest effective agent guided by MC+S results, as per ACSQHC Quality Statement 7 (review of therapy within 48 hours). Antibiotic therapy documentation (indication, dose, route, stop or review date) is required at prescription per Quality Statement 6.

6. Pharmacology and AU PBS notes

Piperacillin/tazobactam (Tazocin, generic): Extended-spectrum penicillin plus beta-lactamase inhibitor. Active against most gram-negatives including Pseudomonas aeruginosa. PBS item 4474T covers IV use in hospitalised patients with severe infection; no streamlined code for HAP specifically. Dose: 4.5 g IV every 6 hours (extended infusion preferred).

Amoxicillin/clavulanate (Augmentin Duo Forte): PBS streamlined item for respiratory tract infections in the community setting; in HAP, hospital supply applies. Oral dose 875/125 mg every 12 hours. Avoid if creatinine clearance below 30 mL/min.

Meropenem (Meronem, generic): Carbapenem; restricted-access antimicrobial in most Australian hospitals requiring infectious diseases or microbiology approval. Dose: 1 g IV every 8 hours (2 g every 8 hours for Pseudomonas aeruginosa or nosocomial CNS infection). Requires local AMS approval.

Vancomycin (generic): Glycopeptide active against MRSA and methicillin-resistant coagulase-negative staphylococci. AU current dosing guidance favours AUC-guided dosing over trough-only monitoring. Initial dose 25 to 30 mg/kg IV (based on actual body weight), then pharmacy-guided dose adjustment. No PBS streamlined code for HAP; hospital formulary item.

Linezolid (Zyvox): Oxazolidinone; PBS authority-required for MRSA infections in hospitalised patients (PBS code 8168X). Oral bioavailability close to 100 percent, making IV-to-oral step-down practical. Monitor full blood count weekly due to myelosuppression risk with courses exceeding 14 days.

7. Complications and monitoring

Complications: - Parapneumonic effusion and empyema thoracis: suspect if patient fails to derogate after 72 hours; investigate with ultrasound-guided pleural aspiration and pH/LDH/glucose analysis. - Lung abscess: complication of aspiration-type HAP with necrotising organisms (Klebsiella, anaerobes); characterised by air-fluid level on chest X-ray and requires prolonged antibiotic therapy of 4 to 6 weeks. - Respiratory failure requiring escalation to high-flow nasal oxygen, non-invasive ventilation, or intubation and mechanical ventilation. - Sepsis and septic shock: HAP is a common precipitant; manage per eTG Antibiotic sepsis pathway and ACSQHC Sepsis Clinical Care Standard. - Recurrence or superinfection with a more resistant organism, particularly after prolonged broad-spectrum therapy. - Antibiotic-associated complications: Clostridioides difficile colitis, acute kidney injury with aminoglycosides or vancomycin, QTc prolongation with fluoroquinolones.

Monitoring schedule: - Clinical review within 48 to 72 hours of antibiotic commencement: reassess response, review MC+S, consider de-escalation. - Procalcitonin every 48 to 72 hours if used to guide duration: target fall of 80 percent from peak. - Renal function every 48 hours in patients receiving vancomycin or aminoglycosides. - Repeat chest X-ray at 72 hours if no clinical improvement; resolution of radiological changes lags clinical improvement by 2 to 4 weeks and should not be used to determine antibiotic duration. - Antibiotic review and documentation of stop or review date per ACSQHC Quality Statements 6 and 7.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.