2.3 Identifying Healthcare-Associated Infection Syndromes

2.3 Identifying Healthcare-Associated Infection Syndromes

Surveillance for Healthcare-Associated Infections (HAIs) is a primary core responsibility of the Infection Preventionist (IP). To ensure consistency across facilities nationwide, the Centers for Disease Control and Prevention (CDC) National Healthcare Safety Network (NHSN) establishes standardized, objective surveillance criteria. IPs must master the distinction between surveillance definitions and clinical diagnoses.

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Surveillance Definitions vs. Clinical Diagnosis

Core NHSN Timing Principles

• Date of Event (DOE): The date when the last element used to meet the NHSN infection criterion occurred within the Infection Window Period.
• Infection Window Period (IWP): A 7-calendar-day period defined as the 3 calendar days before, the day of, and the 3 calendar days after the first positive diagnostic test (e.g., culture, lab test, imaging).
• Healthcare-Associated Infection (HAI) Determination: An infection is designated as an HAI if the Date of Event occurs on or after the 3rd calendar day of admission (where Day 1 is the calendar day of facility admission). Infections occurring on Day 1 or Day 2 are classified as Community-Acquired Infections (CAI).
• Repeat Infection Location (RIL): A 14-calendar-day timeframe during which no new infection of the same type can be reported.

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Central Line-Associated Bloodstream Infection (CLABSI)

A CLABSI is a primary bloodstream infection (BSI) in a patient who had a central line in place for >2 calendar days on the Date of Event, with the line in place on the Date of Event or the day before.

NHSN Definition of a Central Line

An intravascular catheter that terminates at or close to the heart or in one of the great vessels (e.g., superior vena cava, inferior vena cava, subclavian vein, internal jugular vein, femoral vein) used for infusion, blood withdrawal, or hemodynamic monitoring. Pacemaker wires, arterial lines, and peripheral IVs are not central lines.

Diagnostic Criterion Pathways

1. Criterion 1 (Recognized Pathogen): Patient has a recognized pathogen (e.g., Staphylococcus aureus, Enterococcus spp., Pseudomonas aeruginosa, Candida spp.) isolated from one or more blood cultures, AND the pathogen is not related to an infection at another anatomical site.
2. Criterion 2 (Common Commensal): Patient has a common skin commensal (e.g., Coagulase-Negative Staphylococci [CoNS], Corynebacterium spp., Cutibacterium acnes) isolated from two or more blood cultures drawn on the same or consecutive days, PLUS at least one of the following signs/symptoms: fever (>38.0°C), chills, or hypotension.

Rule-Outs & Secondary BSI

• Secondary Bloodstream Infection: A BSI is considered secondary (and NOT a CLABSI) if there is a primary infection at another body site (e.g., positive urine culture matching blood culture in CAUTI, or positive sputum culture matching blood culture in pneumonia) that meets NHSN criteria within the Infection Window Period.
• Mucosal Barrier Injury LCBI (MBI-LCBI): A specialized subset of BSI occurring in severely immunocompromised patients (e.g., post-allogeneic hematopoietic stem cell transplant or severe neutropenia with absolute neutrophil count <500/µL) where gut translocation of normal GI flora (e.g., Enterococcus faecium, Escherichia coli) occurs. These are classified as MBI-LCBI rather than standard CLABSI.

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Catheter-Associated Urinary Tract Infection (CAUTI)

A CAUTI is an infection of the urinary tract in a patient with an indwelling urinary catheter (Foley) in place for >2 calendar days on the Date of Event (and catheter present on the Date of Event or removed the day before).

NHSN CAUTI Diagnostic Criteria

All three of the following criteria must be met:

1. Indwelling Catheter Requirement: Indwelling urinary catheter in place for >2 calendar days on the Date of Event.
2. Clinical Signs / Symptoms: Patient exhibits at least one of the following:
   • Fever (>38.0°C)
   • Suprapubic tenderness*
   • Costovertebral angle pain or tenderness*
   • Urinary urgency, frequency, or dysuria (Note: urgency, frequency, dysuria can only be used if the urinary catheter has been removed)
3. Laboratory Requirement: Urine culture demonstrating ≥10^5 Colony-Forming Units (CFU)/mL of no more than two species of microorganisms.

[Indwelling Catheter >2 Days] + [Fever / Suprapubic Pain] + [Urine Culture >=10^5 CFU/mL (<=2 species)] = CAUTI

Asymptomatic Bacteriuria (ASB)

Isolation of bacteria in urine (even ≥10^5 CFU/mL) in the absence of documented clinical signs or symptoms does NOT meet CAUTI criteria. ASB should not be treated with antibiotics or reported to NHSN as a CAUTI.

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Ventilator-Associated Events (VAE)

VAE surveillance applies to adult patients (≥18 years) in critical care units receiving mechanical ventilation for >2 calendar days. NHSN utilizes a objective, three-tiered surveillance framework to eliminate subjective radiograph interpretations.

  [Tier 1: VAC] (Oxygenation Deterioration: PEEP / FiO2 increase)
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       v
  [Tier 2: IVAC] (VAC + Temp/WBC abnormality + 4 days of Antimicrobials)
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       v
  [Tier 3: PVAP] (IVAC + Purulent Secretions or Positive Lab/Culture)

VAE Tiered Hierarchy

1. Tier 1: Ventilator-Associated Condition (VAC)
   • Patient demonstrates baseline stability or improvement on mechanical ventilation defined by ≥2 consecutive calendar days of stable or decreasing daily minimum PEEP (cmH2O) or minimum FiO2.
   • Followed by an acute oxygenation deterioration: an increase in daily minimum PEEP by ≥3.0 cmH2O OR an increase in daily minimum FiO2 by ≥20 points (0.20) sustained for ≥2 consecutive calendar days.
2. Tier 2: Infection-related Ventilator-Associated Complication (IVAC)
   • Patient meets VAC criteria PLUS:
   • Temperature abnormality (<36.0°C or >38.0°C) OR white blood cell count abnormality (WBC ≥12,000/µL or ≤4,000/µL), AND
   • Initiation of one or more new qualifying antimicrobial agents continued for ≥4 consecutive calendar days.
3. Tier 3: Possible Ventilator-Associated Pneumonia (PVAP)
   • Patient meets IVAC criteria PLUS laboratory or microscopic evidence of respiratory infection:
   • Purulent respiratory secretions (≥25 neutrophils and ≤10 squamous epithelial cells per low-power field), OR
   • Positive quantitative or semi-quantitative culture from endotracheal aspirate (≥10^5 CFU/mL), bronchoalveolar lavage/BAL (≥10^4 CFU/mL), or protected specimen brush (≥10^3 CFU/mL).

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Surgical Site Infections (SSI)

SSIs are infections related to a surgical procedure occurring within a specified surveillance window.

Surveillance Timeframes

• 30-Day Surveillance: Standard for most surgical procedures without implants.
• 90-Day Surveillance: Applies to specific deep incisional or organ/space procedures involving permanent implants or prostheses (e.g., total hip arthroplasty, total knee arthroplasty, coronary artery bypass graft [CABG], craniotomy, spinal fusion).

Anatomical SSI Classifications