Healthcare-Associated Infections
A Step 2 CK–focused lesson on healthcare-associated infections covering CLABSI, CAUTI, VAP/HAP, SSI, and C. difficile — organism, exposure clue, and next-best-step management for each, with board vignettes and current IDSA guidance. Emphasizes source control plus syndrome-tailored empiric coverage and the 2021 IDSA/SHEA update making fidaxomicin the preferred agent (oral vancomycin an acceptable alternative) for C. difficile.
Overview & Epidemiology
Healthcare-associated infections (HAIs) are infections that are neither present nor incubating at admission — defined as arising ≥48 hours after hospitalization (or within 30 days of surgery, up to 90 days when prosthetic material is implanted, for surgical site infections). Four device-associated syndromes dominate the exam: central line–associated bloodstream infection (CLABSI), catheter-associated UTI (CAUTI), ventilator-associated pneumonia (VAP), and surgical site infection (SSI) — plus *Clostridioides difficile*, the leading cause of infectious healthcare-associated diarrhea.
Always suspect multidrug-resistant organisms (MRSA, VRE, ESBL-producing and carbapenem-resistant Enterobacterales, Pseudomonas, Acinetobacter): prior antibiotics and prolonged stay select for them. The board reasoning chain is consistent — identify the device/exposure → name the likeliest organism → choose the next best step, which is usually source control (remove or exchange the device) plus empiric coverage tailored to the syndrome and local resistance.
- Timing: HAI = onset ≥48 h after admission; SSI within 30 days (up to 90 days if prosthetic material implanted)
- CLABSI: coagulase-negative staph (S. epidermidis) most common; also S. aureus, enterococci, Candida. Paired peripheral + catheter cultures with differential time-to-positivity ≥2 h implicates the line
- CAUTI: *E. coli* most common; do NOT treat asymptomatic bacteriuria except in pregnancy or before a urologic procedure
- VAP/HAP: onset ≥48 h after intubation/admission; Pseudomonas, MRSA, gram-negative rods
- SSI: *S. aureus* most common overall
- Empiric vancomycin covers MRSA + coag-negative staph; add an antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, meropenem) when gram-negatives are a concern
- Prevention beats treatment: hand hygiene, chlorhexidine skin prep, sterile insertion bundles, and daily review — "does this device still need to be in?" → early removal
Comparison — Organism · Exposure · Treatment
| Syndrome | Device / exposure | Top organism(s) | Empiric management |
|---|---|---|---|
| CLABSI | Central venous catheter | Coag-neg staph, S. aureus, Candida | Vancomycin; remove line for S. aureus / Pseudomonas / Candida; echinocandin for candidemia |
| CAUTI | Indwelling Foley | E. coli, Enterococcus, Candida | Remove/replace catheter; treat only if symptomatic; agent per local resistance |
| VAP / HAP | Mechanical ventilation | Pseudomonas, MRSA, Klebsiella/Enterobacter, Acinetobacter | Vancomycin or linezolid + antipseudomonal β-lactam (pip-tazo, cefepime, meropenem) |
| SSI | Recent surgery | S. aureus (incl. MRSA), coag-neg staph | Open/drain wound; vancomycin ± gram-neg/anaerobic coverage by site |
| *C. difficile* | Recent antibiotics, PPI | Clostridioides difficile | Oral fidaxomicin (preferred) or oral vancomycin; stop offending antibiotic |
Vignette: A 62-year-old man on chemotherapy through a tunneled central catheter spikes a fever to 39.2°C with rigors. There is no localizing source and the exit site looks clean. Paired blood cultures (catheter + peripheral) grow gram-positive cocci in clusters, with the catheter bottle positive 3 hours before the peripheral one; speciation returns *S. aureus*.
Diagnosis: CLABSI — differential time-to-positivity ≥2 h implicates the catheter as the source.
Next best step:
- Start empiric IV vancomycin (covers MRSA + coag-negative staph)
- Remove the catheter — S. aureus, Pseudomonas, and Candida CLABSI mandate line removal (also for persistent bacteremia, septic shock, endocarditis, or suppurative thrombophlebitis)
- Obtain echocardiography (TTE/TEE) to exclude endocarditis in S. aureus bacteremia and repeat cultures to document clearance
Vignette: A 58-year-old man intubated for ARDS develops, on ventilator day 5, a new fever, purulent secretions, a rising oxygen requirement, and a new left-lower-lobe infiltrate; WBC 16,500.
Diagnosis: Ventilator-associated pneumonia — new infiltrate plus systemic signs arising ≥48 h after intubation. Obtain a lower-respiratory sample (endotracheal aspirate or BAL) for culture before starting antibiotics.
Next best step: Begin empiric therapy covering:
- MRSA → vancomycin or linezolid, plus
- Pseudomonas → an antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, or meropenem)
Add a second antipseudomonal agent (aminoglycoside or antipseudomonal fluoroquinolone) when there is high resistance risk or septic shock. De-escalate at 48–72 h based on culture and susceptibility results.
Vignette: A 74-year-old woman admitted for pneumonia and treated with ceftriaxone develops profuse watery diarrhea (8 stools/day), lower abdominal cramping, WBC 18,000, and low-grade fever on hospital day 6.
Diagnosis: Clostridioides difficile infection. Confirm on unformed stool with NAAT (toxin-gene PCR) or a GDH antigen + toxin EIA algorithm. Do not test formed stool and do not perform test-of-cure.
Next best step:
- Stop the inciting antibiotic (ceftriaxone) if clinically possible
- Start oral fidaxomicin (preferred in the 2021 IDSA/SHEA update) or oral vancomycin; reserve metronidazole for when neither is available
- Fulminant disease (hypotension/shock, ileus, or toxic megacolon) → high-dose oral vancomycin + IV metronidazole, add rectal vancomycin if ileus, and surgical consult for possible colectomy
- Avoid antimotility agents (risk of ileus/megacolon)
- Risk factors: recent antibiotics (clindamycin, fluoroquinolones, cephalosporins, β-lactam/β-lactamase inhibitors), PPIs, age >65, prolonged hospitalization
- Diagnosis: test only diarrheal (unformed) stool — NAAT (PCR) for toxin gene, or GDH + toxin EIA algorithm; no test-of-cure
- Severity: non-severe → severe (WBC ≥15,000 or Cr ≥1.5 mg/dL) → fulminant (hypotension/shock, ileus, or toxic megacolon)
- First-line (2021 IDSA/SHEA): oral fidaxomicin (now preferred) or oral vancomycin; reserve metronidazole for when neither is available
- Recurrence: fidaxomicin or tapered/pulsed vancomycin; bezlotoxumab (anti–toxin B monoclonal) reduces recurrence; fecal microbiota transplant for multiply recurrent disease
- Infection control: contact precautions + soap-and-water hand washing — alcohol gel does NOT kill spores
Antibiotic classes most classically implicated in *C. difficile* infection — the "4 C's":
- Clindamycin
- Cephalosporins (especially 3rd/4th generation)
- Ciprofloxacin / fluoroquinolones
- Co-amoxiclav (amoxicillin-clavulanate)
Other broad-spectrum agents (carbapenems, piperacillin-tazobactam) also raise risk. Hand-hygiene pearl: spores survive alcohol → wash with soap and water, not just gel.
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