Healthcare Associated Infections

1. Introduction and Definition

Healthcare-associated infections (HAIs), formerly known as nosocomial infections, are infections that occur as a consequence of healthcare interventions.

• Definition: An infection acquired by a patient during the process of care in a hospital or other healthcare facility (e.g., ambulatory surgical centers, dialysis centers, long-term care facilities) that was not present or incubating at the time of admission.
• Timeframe: Typically, infections manifesting 48 hours or more after admission are considered HAIs.
• Scope: The term also encompasses occupational infections acquired by healthcare workers (HCWs).
• Neonatal Context: Infections acquired by neonates during passage through the birth canal are considered HAIs by CDC definitions, distinct from transplacental (congenital) infections.

2. Epidemiology and Burden

HAIs represent a major public health crisis, leading to increased morbidity, mortality, prolonged length of stay (LOS), and escalated healthcare costs.

• Prevalence: Approximately 1 in 31 hospitalized patients experiences at least one HAI on any given day.
• Pediatric Risk: Rates are significantly higher in Pediatric Intensive Care Units (PICU) and Neonatal Intensive Care Units (NICU) compared to general pediatric wards due to the frequent use of invasive devices and host vulnerability.
• Indian Scenario: In India, HAIs are predominantly caused by multidrug-resistant (MDR) Gram-negative bacilli, creating significant therapeutic challenges.

3. Pathogenesis and Transmission

The development of an HAI requires a susceptible host, an infectious agent, and a mode of transmission.

• Sources of Infection:
  • Endogenous: The majority of infections arise from the patient's own endogenous flora (skin, GI tract) which translocate to sterile sites or colonize invasive devices.
  • Exogenous: Acquired from the healthcare environment, equipment (fomites), or healthcare personnel.
• Modes of Transmission:
  • Contact Transmission: The most common route.
    • Direct: Physical transfer between an infected person and a susceptible host (e.g., scabies, HSV).
    • Indirect: Transfer via an intermediate object, most notably the contaminated hands of healthcare workers or medical equipment (e.g., C. difficile, MRSA, VRE, Gram-negatives).
  • Droplet Transmission: Large respiratory droplets (>5 µm) traveling short distances (<3 feet), generated by coughing/sneezing (e.g., B. pertussis, N. meningitidis, Influenza, Mumps).
  • Airborne Transmission: Small particles (<5 µm) that remain suspended in the air for long periods and travel long distances (e.g., Tuberculosis, Measles, Varicella).
• Biofilms: A critical pathogenetic mechanism for device-associated infections. Microorganisms adhere to the surface of catheters or implants and form organized communities (biofilms) that protect them from host defenses and antimicrobial therapy.

4. Etiology

The microbial spectrum of HAIs varies by geography, hospital unit, and patient population.

• ESKAPE Pathogens: A group of high-priority MDR pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species.
• Gram-Negative Bacilli (GNB):
  • In India and many developing countries, GNB are the predominant cause of HAIs.
  • Common agents: Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacter spp..
  • Resistance: High rates of Extended-Spectrum Beta-Lactamase (ESBL) production and Carbapenem-Resistant Enterobacteriaceae (CRE) are major concerns.
• Gram-Positive Bacteria:
  • Staphylococcus aureus: Including Methicillin-Resistant S. aureus (MRSA), a major cause of surgical site infections (SSI) and ventilator-associated pneumonia (VAP).
  • Coagulase-Negative Staphylococci (CoNS): The most common cause of catheter-related bloodstream infections (CRBSI) in neonates and children.
  • Enterococcus spp.: Including Vancomycin-Resistant Enterococci (VRE).
• Fungi:
  • Candida spp. (especially non-albicans species like C. auris and C. parapsilosis) are emerging as significant causes of bloodstream infections in NICUs and ICUs.
• Viruses:
  • Respiratory viruses (RSV, Influenza, Adenovirus, Parainfluenza) and gastrointestinal viruses (Rotavirus, Norovirus) are common causes of outbreaks in pediatric wards.
• Special Pathogens: Clostridioides difficile (formerly Clostridium) is the leading cause of healthcare-associated infectious diarrhea.

5. Common Clinical Syndromes

HAIs are frequently associated with the use of invasive medical devices.

A. Central Line-Associated Bloodstream Infections (CLABSI)

• Definition: A primary bloodstream infection in a patient with a central line in place for >2 days on the date of the event, with no other identifiable source.
• Pathogenesis: Organisms migrate from the skin insertion site along the external surface of the catheter or are introduced intraluminally via contaminated hubs/infusates.
• Common Pathogens: CoNS (most common), S. aureus, Enteric GNB, Candida.
• Diagnosis: Requires positive blood culture with a matching organism from the catheter tip or differential time to positivity (catheter culture turns positive >2 hours before peripheral culture).

B. Catheter-Associated Urinary Tract Infections (CAUTI)

• Definition: Symptomatic UTI in a patient with an indwelling urinary catheter in place for >2 days.
• Pathogenesis: Biofilm formation on the catheter surface facilitates ascending infection from perineal flora or contaminated hands.
• Common Pathogens: E. coli (most common), Klebsiella, Pseudomonas, Enterococcus, Candida.
• Clinical: Fever, suprapubic tenderness, rigors; often asymptomatic bacteriuria (which should generally not be treated).

C. Ventilator-Associated Pneumonia (VAP)

• Definition: Pneumonia occurring >48 hours after endotracheal intubation.
• Risk Factors: Prolonged ventilation, re-intubation, aspiration, supine positioning.
• Microbiology: Early-onset (<4 days) often involves community flora (S. pneumoniae, H. influenzae); late-onset (>4 days) involves MDR pathogens (P. aeruginosa, MRSA, Acinetobacter).

D. Surgical Site Infections (SSI)

• Definition: Infection occurring at the incision site within 30 days of surgery (or up to 90 days for implants).
• Classification: Superficial incisional, Deep incisional, or Organ/Space.
• Pathogens: S. aureus (most common), CoNS, GNB, Enterococci.

E. Clostridioides difficile Infection (CDI)

• Pathogenesis: Antibiotic exposure disrupts normal gut flora, allowing colonization and toxin production by C. difficile.
• Transmission: Fecal-oral route via spores which are resistant to alcohol and survive in the environment for months.
• Clinical: Watery diarrhea, fever, abdominal pain, leukocytosis; can progress to pseudomembranous colitis.

6. Diagnosis

Diagnosis relies on a combination of clinical signs and microbiologic evidence.

• Surveillance vs. Clinical Definitions: NHSN surveillance definitions are used for reporting and benchmarking (e.g., CLABSI) but may differ from clinical diagnoses requiring treatment.
• Cultures: Essential for targeting therapy. Blood, urine, endotracheal aspirates, and wound swabs should be collected before initiating antibiotics.
• Interpretation: Distinguishing colonization from true infection is critical, especially for cultures from non-sterile sites (e.g., trachea, urine, drains). Isolation of CoNS from a single blood culture may represent contamination.

7. Management Principles

• Empiric Therapy: Initiate broad-spectrum antibiotics promptly in critically ill patients, guided by local antibiograms and risk factors for MDR organisms.
• Targeted Therapy: De-escalate to narrower-spectrum agents once culture and sensitivity results are available to reduce selection pressure.
• Source Control: Removal of infected devices (CVCs, urinary catheters) and drainage of abscesses are crucial for cure.
• Treatment of Specific HAIs:
  • CLABSI: Vancomycin + Anti-pseudomonal Beta-lactam is a common empiric choice. Duration 7–14 days typically.
  • CDI: Oral Vancomycin or Fidaxomicin are first-line agents. Metronidazole is an alternative for non-severe cases if others are unavailable.
  • MDR Gram-negatives: May require Colistin, Polymyxin B, or newer combinations (Ceftazidime-Avibactam).

8. Prevention and Infection Control

Prevention is the cornerstone of HAI management, relying on "bundles" of care and strict adherence to protocols.

A. Standard Precautions

• Hand Hygiene: The single most important measure to prevent HAI transmission.
  • Five Moments: (1) Before touching a patient, (2) Before clean/aseptic procedures, (3) After body fluid exposure risk, (4) After touching a patient, (5) After touching patient surroundings.
  • Method: Alcohol-based hand rub is preferred for most situations; soap and water must be used when hands are visibly soiled or for spore-forming organisms like C. difficile.
• Personal Protective Equipment (PPE): Gloves, gowns, masks, and eye protection based on risk assessment.
• Respiratory Hygiene/Cough Etiquette: Covering mouth/nose, hand hygiene, and masking symptomatic persons.
• Safe Injection Practices: Use of sterile, single-use disposables; never recapping needles.

B. Transmission-Based Precautions

Used in addition to standard precautions for specific pathogens.

• Contact Precautions: Gown and gloves. Used for MDR organisms (MRSA, VRE, CRE), C. difficile, Scabies, Rotavirus.
• Droplet Precautions: Surgical mask. Used for Influenza, Pertussis, Mumps, N. meningitidis.
• Airborne Precautions: N95 respirator and negative pressure room. Used for TB, Measles, Varicella.

C. Prevention Bundles

Evidence-based sets of interventions implemented together to improve outcomes.

• CLABSI Bundle:
  • Hand hygiene.
  • Maximal sterile barrier precautions during insertion.
  • Chlorhexidine skin antisepsis (avoid in very pre-term infants or use with caution).
  • Optimal site selection (avoid femoral).
  • Daily review of line necessity and prompt removal.
• VAP Bundle:
  • Head of bed elevation (30–45 degrees).
  • Daily sedation vacation and assessment of readiness to extubate.
  • Oral hygiene with chlorhexidine.
  • Subglottic suctioning.
• CAUTI Bundle:
  • Insert only for appropriate indications.
  • Maintain closed drainage system.
  • Keep bag below bladder level.
  • Remove catheter as soon as no longer necessary.

D. Antimicrobial Stewardship Program (ASP)

• Coordinated interventions to optimize antimicrobial use, improve patient outcomes, and minimize resistance (e.g., prospective audit and feedback, preauthorization).
• Goal: "Right drug, right dose, right duration, right route".

E. Environmental Hygiene

• Proper cleaning and disinfection of surfaces and equipment.
• C. difficile requires sporicidal agents (e.g., bleach).
• Air and water quality management (e.g., preventing Legionella, Aspergillus).

F. Surveillance

• Systematic collection, analysis, and interpretation of HAI data (e.g., using NHSN criteria) to guide infection control policies and detect outbreaks.