What are the diagnostic criteria and treatment options for Healthcare-Associated Infections (HAIs)?

Diagnosing Healthcare-Associated Infections (HAIs)

Healthcare-associated infections are diagnosed based on temporal criteria (>48 hours after hospital admission or within 7 days post-discharge) combined with clinical evidence of infection and positive microbiological testing, with the specific diagnostic approach varying by infection type. 1

Temporal Diagnostic Criteria

The fundamental diagnostic requirement is timing: infections must develop more than 48 hours after hospital admission OR within 7 days after hospital discharge to be classified as healthcare-associated. 1

Expanded Healthcare-Associated Risk Factors

Beyond the standard 48-hour/7-day rule, consider HAI diagnosis in patients with: 1

• Recent hospitalization within 90 days 1
• Nursing facility residence 1
• Aggressive medical therapies at home within 30 days (e.g., IV antibiotics, wound care, chemotherapy) 1
• Invasive outpatient procedures within 30 days (e.g., hemodialysis, endoscopy) 1
• Presence of invasive devices at admission (central lines, urinary catheters, ventilators) 2, 1
• History of MRSA colonization or infection 2, 1
• Prior surgery or hospitalization 2, 1

Site-Specific Diagnostic Approaches

Intra-Abdominal HAIs

Diagnosis requires both clinical evidence AND microbiological confirmation: 2

• Clinical criteria: Fever, abdominal pain, peritoneal signs, or evidence of organ dysfunction 2
• Imaging: Ultrasonography as first-line for suspected acute cholecystitis; CT for complex infections 2
• Microbiological work-up: Culture infected fluid to identify pathogens and guide antimicrobial therapy 2
• Expected pathogens: Multidrug-resistant organisms including P. aeruginosa, Acinetobacter, ESBL-producing Enterobacteriaceae, MRSA, enterococci, and Candida species 2

Clostridioides difficile Infection (CDI)

CDI diagnosis requires BOTH: 2

1. Presence of diarrhea OR evidence of megacolon/severe ileus 2
2. Positive laboratory test (toxin EIA or NAAT) OR pseudomembranes on endoscopy/histopathology 2

Classification by timing: 2

• Healthcare facility-onset (HO-CDI): Positive test >3 days after admission (day 4 or later) 2
• Community-onset, healthcare facility-associated (CO-HCFA): Positive test within 28 days after discharge 2

Device-Associated HAIs

The most common HAIs are device-related and require specific diagnostic criteria: 3

• Central line-associated bloodstream infections (CLABSI): Positive blood culture with central line in place >48 hours 3
• Catheter-associated urinary tract infections (CAUTI): Positive urine culture (≥10³ CFU/mL) with indwelling catheter >2 days 3
• Ventilator-associated pneumonia (VAP): New infiltrate on chest imaging plus clinical criteria (fever, leukocytosis, purulent secretions) in mechanically ventilated patient >48 hours 3
• Surgical site infections (SSI): Infection at surgical site within 30 days of procedure (or 90 days if implant placed) 2, 3

Microbiological Diagnosis

Culture Requirements

Obtain cultures BEFORE initiating empiric antibiotics whenever possible: 2

• Blood cultures: Minimum 2 sets from separate sites for suspected bacteremia 2
• Site-specific cultures: Infected fluid, tissue, or device tips as appropriate 2
• Repeat cultures: After 48-72 hours of therapy to document clearance in serious infections 4

Antimicrobial Susceptibility Testing

Perform susceptibility testing on all significant isolates to guide therapy: 2

• MIC determination for serious infections (e.g., bacteremia, endocarditis) 5
• Local antibiogram review to understand institutional resistance patterns 2
• Test for specific resistance mechanisms: MRSA, ESBL, carbapenemase production 2

Surveillance and Monitoring

Institutional Surveillance

All healthcare facilities should track healthcare facility-onset (HO) cases using standardized definitions: 2

• Minimum surveillance: HO-CDI cases (>3 days after admission) 2
• Denominator: Patient-days (not admissions) for accurate rate calculation 2
• Risk adjustment: Account for test type sensitivity (NAAT vs. toxin EIA) and community-onset prevalence 2
• Stratification: By hospital location or clinical service when rates exceed baseline 2

Outcome Monitoring

Track severe outcomes attributable to HAIs: 2

• Colectomy 2
• ICU admission 2
• Death 2
• Case-fatality rates (range 2.3-14.4% depending on infection type) 3

Critical Diagnostic Pitfalls

False-Positive Considerations

Distinguish true infection from colonization or contamination: 2

• Mycobacterial pseudo-outbreaks: Often due to contaminated water systems, bronchoscopes, or terminal rinse water rather than true infection 2
• Single positive blood culture: May represent contamination; clinical correlation essential 2

Test Sensitivity Issues

NAAT testing for C. difficile is more sensitive than toxin EIA, leading to higher reported rates: 2

• NAAT detects toxin genes (higher sensitivity) 2
• Toxin EIA detects actual toxin (higher specificity) 2
• Clinical correlation required to distinguish colonization from disease 2

Timing Exceptions

Infections beyond 7 days post-discharge are generally community-acquired UNLESS: 1

• Ongoing home healthcare interventions present 1
• Recent outpatient invasive procedures performed 1
• Surgical site infection related to prior hospitalization 1

Prevention as Diagnostic Context

Understanding prevention strategies informs diagnostic suspicion: 2, 6

• Hand hygiene compliance is the single most important prevention measure 6, 7
• Device removal when no longer necessary reduces infection risk 3, 7
• Multifaceted interventions can reduce HAI rates by 35-55% 2
• Alcohol-based hand rubs are more effective than soap and water for routine hand hygiene 6