Nosocomial infections

1. Introduction and Definition

Nosocomial infections, now more commonly referred to as Healthcare-Associated Infections (HAIs), are infections that occur in patients during the process of care in a hospital or other healthcare facility, which were neither present nor incubating at the time of admission,.

Typically, infections manifesting more than 48 hours after admission are considered nosocomial. These infections represent a significant public health burden, leading to increased morbidity, mortality, prolonged hospital stays, and elevated healthcare costs. In the pediatric population, critically ill children in Pediatric Intensive Care Units (PICUs) and Neonatal Intensive Care Units (NICUs) are at the highest risk.

2. Epidemiology and Risk Factors

The epidemiology of HAIs varies by unit (NICU vs. PICU vs. Wards) and patient population. Data from the National Healthcare Safety Network (NHSN) indicates that approximately 1 in 31 hospitalized patients experiences at least one HAI on any given day.

2.1. Risk Factors

• Host Factors: Prematurity (especially extremely low birth weight), immunocompromised states (oncology, transplant, primary immunodeficiency), malnutrition, and severe underlying illness,.
• Invasive Devices: The most significant risk factors are indwelling medical devices which breach natural barriers. These include Central Venous Catheters (CVCs), urinary catheters, and endotracheal tubes.
• Medications: Prolonged use of broad-spectrum antibiotics (leading to resistance and fungal overgrowth), gastric acid suppression (H2 blockers/PPIs), and immunosuppressive therapy,.
• Environmental Factors: Prolonged hospitalization, overcrowding, and poor hand hygiene compliance among healthcare workers.

3. Etiology and Common Pathogens

HAIs in India and many developing nations are predominantly caused by resistant gram-negative bacilli, though gram-positive organisms and fungi remain significant.

3.1. Bacteria

• Gram-Positive Cocci:
  • Coagulase-Negative Staphylococci (CoNS): S. epidermidis is the most common cause of HAIs, particularly CLABSI in the NICU. It thrives on indwelling devices by forming biofilms,.
  • Staphylococcus aureus: Both Methicillin-Sensitive (MSSA) and Methicillin-Resistant (MRSA) strains are major causes of skin/soft tissue infections, pneumonia, and bacteremia.
  • Enterococcus species: Including Vancomycin-Resistant Enterococci (VRE), are important in patients with prolonged antibiotic exposure.
• Gram-Negative Bacilli (GNB):
  • "ESKAPE" Pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species are highly virulent and resistant.
  • Resistant GNB: Extended-spectrum beta-lactamase (ESBL), AmpC beta-lactamase, and carbapenemase-producing organisms (e.g., Klebsiella, E. coli) are predominant in Indian ICUs,.
  • Pseudomonas aeruginosa: A classic opportunist causing VAP, CLABSI, and UTIs, especially in neutropenic and CF patients.
  • Environmental Pathogens: Stenotrophomonas maltophilia and Burkholderia cepacia affect chronically instrumented or immunocompromised children,.

3.2. Fungi

• Candida species: C. albicans and non-albicans species (e.g., C. parapsilosis, C. glabrata) are leading causes of bloodstream infections in the NICU and PICU. Candida auris is an emerging multidrug-resistant global threat.

3.3. Viruses

• Respiratory viruses (RSV, Influenza, SARS-CoV-2) and gastrointestinal viruses (Rotavirus, Norovirus) are efficiently transmitted in pediatric wards causing nosocomial outbreaks,.

4. Pathogenesis

The pathogenesis of HAIs typically involves three elements: a source, a host, and a mode of transmission.

1. Biofilm Formation: A key mechanism for device-associated infections. Microorganisms (e.g., CoNS, Candida) adhere to the catheter surface, producing an exopolysaccharide matrix that protects them from host defenses and antibiotics,.
2. Translocation: Damage to mucosal barriers (e.g., chemotherapy-induced mucositis) allows endogenous gut flora to enter the bloodstream.
3. Cross-Infection: Transmission via contaminated hands of healthcare workers is the most common mode of spread for pathogens like MRSA and Gram-negative bacilli,.

5. Clinical Syndromes

The most serious and reportable HAIs include:

5.1. Central Line-Associated Bloodstream Infection (CLABSI)

• Definition: A laboratory-confirmed bloodstream infection where a central line was in place for >2 calendar days and is the likely source.
• Etiology: CoNS, S. aureus, Candida, Gram-negatives.
• Clinical Features: Fever, rigors, hemodynamic instability, or inflammation at the exit site. In neonates, signs may be subtle (apnea, bradycardia).

5.2. Ventilator-Associated Pneumonia (VAP)

• Definition: Pneumonia occurring >48 hours after endotracheal intubation.
• Pathogenesis: Aspiration of colonized oropharyngeal or gastric secretions.
• Etiology: P. aeruginosa, S. aureus, Klebsiella.

5.3. Catheter-Associated Urinary Tract Infection (CAUTI)

• Risk: Virtually all patients with an indwelling urinary catheter >30 days develop bacteriuria.
• Etiology: E. coli, Enterococcus, Pseudomonas, Candida,.

5.4. Surgical Site Infections (SSI)

• Infections occurring at the incision site within 30 days of surgery (or up to 1 year with implants). S. aureus is the leading cause.

5.5. Clostridioides difficile Infection (CDI)

• The most common cause of healthcare-associated infectious diarrhea, often triggered by antibiotic use altering the gut microbiome.

6. Diagnosis

Diagnosis requires distinguishing infection from colonization, as mere isolation of bacteria from non-sterile sites (trachea, urine, drains) is not indicative of active disease.

1. Cultures: Blood, urine, CSF, and purulent exudates.
   • CLABSI Diagnosis: Differential time to positivity (DTP) is useful. Growth from a CVC blood sample ≥2 hours before a peripheral culture suggests the catheter is the source.
2. Imaging: Chest X-ray for VAP; Ultrasound/CT for abscesses.
3. Biomarkers: Procalcitonin and CRP may help but lack high specificity for HAIs.
4. Specific Tests: Toxin assays or PCR for C. difficile.

7. Management Principles

7.1. Empiric Antimicrobial Therapy

• Start broad-spectrum antibiotics promptly for suspected sepsis, based on local antibiograms and resistance patterns,.
• Regimens: Often a combination of an anti-pseudomonal beta-lactam (e.g., Piperacillin-Tazobactam, Meropenem) +/- Vancomycin (if MRSA is suspected) +/- Amikacin.
• Candida: Echinocandins (Caspofungin/Micafungin) or Fluconazole are used depending on prior exposure and severity.

7.2. Source Control

• Catheter Removal: Essential for infections caused by S. aureus, Candida, or Pseudomonas, or if there is hemodynamic instability, metastatic infection, or persistent bacteremia,.
• Abscess Drainage: Surgical intervention for collections or infected hardware,.

7.3. Rational Antimicrobial Therapy (De-escalation)

• Once culture results are available (usually 48-72 hours), therapy must be de-escalated to the narrowest effective spectrum to prevent resistance,.

8. Prevention Strategies

Prevention is the cornerstone of HAI management, focusing on breaking the chain of transmission.

8.1. Standard and Transmission-Based Precautions

• Hand Hygiene: The single most important measure. WHO "5 Moments for Hand Hygiene" must be strictly followed using alcohol-based hand rub or soap and water.
• Isolation:
  • Contact: For MDROs (MRSA, VRE), C. difficile, Rotavirus,.
  • Droplet: For Influenza, N. meningitidis, Pertussis.
  • Airborne: For Measles, Varicella, Tuberculosis.

8.2. Care Bundles

"Bundles" are sets of evidence-based practices performed collectively to improve outcomes.

• CLABSI Prevention Bundle:
  • Hand hygiene.
  • Maximal sterile barrier precautions during insertion.
  • Chlorhexidine skin antisepsis (>0.5%).
  • Optimal site selection (avoid femoral).
  • Daily review of line necessity with prompt removal of unnecessary lines.
• CAUTI Prevention: Insert only for appropriate indications, maintain closed drainage, keep bag below bladder level, and remove early.
• VAP Prevention: Head of bed elevation (30-45 degrees), oral care with chlorhexidine, sedation vacations, and daily assessment of readiness to extubate.

8.3. Antimicrobial Stewardship (ASP)

• ASPs aim to optimize antibiotic selection, dose, and duration to minimize toxicity and resistance.
• Strategies include Preauthorization (restricting certain high-end antibiotics) and Prospective Audit and Feedback (reviewing cases after 48-72 hours to recommend de-escalation).

8.4. Environmental Cleaning

• Routine disinfection of high-touch surfaces and medical equipment (stethoscopes) is vital. C. difficile requires sporicidal agents (e.g., chlorine),.