Hospital-Acquired Infections (HAI): Causes and Prevention in ICU

Long Answer — MD Anaesthesia Examination

DEFINITION

CLASSIFICATION OF HAI IN ICU

PART I: CAUSES OF HOSPITAL-ACQUIRED INFECTIONS

A. Host-Related Factors

1. Critical illness — altered immune defences, malnutrition, underlying comorbidities (diabetes, malignancy, renal failure, COPD)
2. Extremes of age — neonates and the elderly have impaired immunity
3. Immunosuppression — steroids, chemotherapy, immunomodulatory therapy
4. Disrupted skin/mucosal barriers — surgical wounds, intravascular catheters, endotracheal tubes, urinary catheters
5. Altered microbiome — broad-spectrum antibiotics promote colonisation with resistant organisms

B. Pathogen-Related Factors

C. Device/Procedure-Related Factors

1. Endotracheal tube — bypasses mucociliary clearance; pooling of secretions above the cuff leads to microaspiration → VAP
2. Nasotracheal intubation — blocks sinus ostia; ~95% of patients develop radiographic sinusitis after 1 week (vs. ~25% with oral intubation)
3. Central venous catheters — skin colonisation, hub contamination, hematogenous seeding, contaminated infusate; biofilm formation on catheter surface
4. Urinary bladder catheter — bacteriuria increases with duration; ~5% develop bacteremia
5. Nasogastric tube — disrupts gastroesophageal barrier; increases aspiration risk

D. Environmental and Healthcare System Factors

1. Hand hygiene non-compliance — the single most important preventable cause of cross-transmission
2. Contaminated equipment and surfaces — inadequate disinfection/sterilisation
3. Crowding and understaffing — particularly relevant during surges (e.g., COVID-19 pandemic caused CLABSI rates to rise 28–91%)
4. Hospital building infrastructure — HVAC systems (Legionella, Aspergillus), water distribution, construction dust
5. Prolonged antibiotic use — selection pressure for resistant organisms and C. difficile
6. Parenteral nutrition (PN) — a major risk factor for invasive Candida infection
7. Acid suppression therapy — allows gastric bacterial overgrowth, increasing aspiration/VAP risk

E. Iatrogenic Factors

• Emergency/unsterile device placement (field lines)
• Unnecessary invasive procedures
• Prolonged duration of indwelling devices without daily review
• Inappropriate antibiotic prescribing promoting resistance

PART II: PREVENTION OF HAI IN ICU

1. PREVENTION OF VENTILATOR-ASSOCIATED PNEUMONIA (VAP)

Non-pharmacological Measures:

• Semirecumbent positioning: Head-of-bed elevation ≥30° — reduces microaspiration of gastric contents (simple, no cost, strong evidence)
• Strict hand hygiene between all patient contacts
• Oral decontamination with chlorhexidine gluconate — reduces oropharyngeal bacterial burden; likely reduces VAP incidence
• Subglottic suctioning endotracheal tubes — meta-analysis supports reduction in VAP incidence and shorter ICU/hospital length of stay
• Ventilator circuit management — change only when visibly soiled; avoid unnecessary circuit breaks
• Early weaning/extubation — minimise duration of mechanical ventilation; daily spontaneous breathing trials
• Non-invasive ventilation (NIV) preference where clinically appropriate — avoids intubation altogether

Pharmacological Controversies:

• GI acid suppression — acid-suppressive agents increase gastric bacterial overgrowth and VAP risk; use only in high-risk patients (coagulopathy, mechanical ventilation). Sucralfate is an alternative with less acid suppression
• Selective Digestive Decontamination (SDD) — nonabsorbable enteral antibiotics; growing evidence supports use but remains controversial due to antibiotic resistance concerns

Diagnostic Stewardship:

• Invasive quantitative cultures (tracheal aspirate preferred per IDSA; BAL/protected brush as alternative): diagnose VAP only when ≥10⁴ CFU/mL (BAL) or ≥10³ CFU/mL (protected brush)
• De-escalation therapy: Start broad spectrum empirically after cultures taken; narrow or stop based on 48–72 h culture results — reduces resistance emergence
• Duration: 8-day course is effective; consider longer for non-lactose-fermenting GNRs (Pseudomonas)

2. PREVENTION OF CATHETER-RELATED BLOODSTREAM INFECTION (CRBSI/CLABSI)

Insertion Bundle:

1. Hand hygiene — wash hands before insertion
2. Maximal sterile barrier precautions: sterile gown, gloves, mask, cap + large full-body drape for the patient
3. Chlorhexidine-alcohol skin antisepsis — superior to povidone-iodine or alcohol alone
4. Optimal site selection:
   • Subclavian vein → lowest infection and DVT risk (but highest mechanical complication risk)
   • Internal jugular → intermediate
   • Femoral vein → highest infection risk; reserve for emergency/coagulopathy
5. Ultrasound guidance — reduces attempts and trauma
6. Replace any catheter placed under emergency/unsterile conditions as soon as patient allows

Maintenance Bundle:

3. PREVENTION OF CATHETER-ASSOCIATED URINARY TRACT INFECTION (CAUTI)

• Strict aseptic technique during catheter insertion
• Rigorous hand hygiene
• Minimise duration of catheterisation — review necessity daily
• Use bladder catheters only when strictly indicated (not for convenience)
• Maintain closed drainage system; keep bag below bladder level
• Antimicrobial/antiseptic catheter coatings — insufficient evidence to recommend routinely
• Consider intermittent catheterisation as alternative to indwelling catheter where feasible

4. PREVENTION OF INVASIVE FUNGAL INFECTION (IFI)

• CVCs, PN, broad-spectrum antibiotics, recent abdominal surgery (anastomotic leak, GI perforation), dialysis-dependent renal failure, steroids

• Limit risk factors: shorten CVC duration, minimise PN, restrict antibiotics
• Prophylactic fluconazole — may be considered in high-risk surgical ICU patients
• Prompt diagnosis: β-D-glucan assay (80% sensitive/specific for Candida/Aspergillus); whole-blood PCR (sensitivity >90%) for early detection
• Candida in urine/sputum alone does not mandate treatment; often resolves with catheter removal
• Treat promptly when invasive infection confirmed — delayed treatment increases dissemination and mortality

5. PREVENTION OF ICU-ACQUIRED SINUSITIS

• Prefer orotracheal over nasotracheal intubation — reduces sinusitis from 95% to ~25% at one week
• Remove nasal tubes (NG tube, nasotracheal tube) as early as possible
• Suspect sinusitis as cause of fever of unknown origin in surgical ICU

6. PREVENTION OF C. DIFFICILE INFECTION (CDI)

• Antibiotic stewardship — restrict broad-spectrum antibiotics; de-escalate rapidly
• Contact precautions — gown and gloves; isolate affected patients
• Hand hygiene with soap and water (alcohol gel is INEFFECTIVE against C. difficile spores — handwashing physically removes spores)
• Environmental cleaning with sporicidal agents (e.g., bleach-based solutions)
• Avoid proton pump inhibitors unless clearly indicated

7. GENERAL ICU INFECTION PREVENTION STRATEGIES

Care Bundles and Protocols:

• Implementing a simple ventilator care bundle reduces VAP and antibiotic utilisation
• Central line bundle (insertion + maintenance) → ~46% reduction in CLABSI nationally

Antimicrobial Stewardship:

• Local antibiogram-guided empiric therapy
• Routine de-escalation after 48–72 h culture results
• Avoid unnecessary prophylactic antibiotics

Environmental and Structural Measures (Table 83.1 — Tietz):

Infection Prevention and Control (IPC) Programme:

• Led by physician hospital epidemiologist or trained IC nurse
• Surveillance, outbreak investigation, isolation precautions
• Staff education and competency-based training
• Emergency preparedness for novel pathogens/bioterrorism

EMPIRIC ANTIBIOTIC REGIMENS FOR COMMON ICU INFECTIONS

Antibiotic selection must account for local antibiograms. All regimens should be narrowed once culture results are available.

SUMMARY TABLE: HAI PREVENTION BUNDLES IN ICU

CONCLUSION

• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e — Chapter 57 (Critical Care Medicine)
• Miller's Anesthesia, 2-Volume Set, 10e — Infectious Complications of CVC
• Current Surgical Therapy, 14e — CLABSI Chapter
• Tietz Textbook of Laboratory Medicine, 7e — Infection Prevention and Control
• Goldman-Cecil Medicine, International Edition — HAP/VAP Epidemiology