Coagulase-Negative Staphylococcus (CoNS) - Infection Management

Overview of Clinically Relevant Species

• S. epidermidis - most common; biofilm-forming; healthcare-associated bacteremia and device infections
• S. lugdunensis - most virulent; behaves more like S. aureus; native valve endocarditis
• S. haemolyticus - drug-resistant; ICU infections
• S. saprophyticus - urinary tract infections in young women
• S. schleiferi - emerging pathogen

Step 1: Distinguishing True Infection from Contamination

• Two or more blood cultures positive for the same species from different sites
• Positive culture from blood and another sterile site (CSF, joint fluid) with matching susceptibility patterns
• Growth in continuously monitored blood culture system within 15 hours
• Compatible clinical findings (fever, hemodynamic instability, etc.)
• Intravascular catheter in place >3 days
• Identical or similar genotypes among isolates

Step 2: Antibiotic Selection by Susceptibility

Key Principle: Methicillin Resistance is the Rule

"More than 90% of health care-associated CoNS strains are methicillin resistant. Methicillin-resistant strains are resistant to all beta-lactam drugs, including cephalosporins (except ceftaroline), and usually several other drug classes."

• Red Book 2021, p. 1075

First-Line: Vancomycin

Exception - S. lugdunensis

• Nafcillin (or oxacillin) for MSSA strains
• Vancomycin for penicillin-allergic patients or resistant strains
• Managed like S. aureus infections (Red Book 2021)

Methicillin-Susceptible CoNS (rare, mostly S. lugdunensis)

• Nafcillin 2g IV q4h or oxacillin
• Cefazolin as an alternative to semisynthetic penicillins
• Higher cure rates with beta-lactams than vancomycin

Alternative Agents When Vancomycin Cannot Be Used

Step 3: Management by Clinical Scenario

A. Catheter-Related Bloodstream Infection (CRBSI)

1. Remove the catheter - this is the most important intervention. Biofilm prevents antibiotic penetration.
2. Antibiotic course if catheter removed and bacteremia resolves promptly:
   • Immunocompetent host: 5 days of IV antibiotics (vancomycin)
   • S. lugdunensis: treat like S. aureus CRBSI (longer course, 14 days minimum)
3. Antimicrobial lock therapy (e.g., vancomycin lock) may allow catheter salvage in tunneled central lines in select cases, though evidence in pediatrics is limited
4. If blood cultures remain positive >3-5 days after appropriate therapy: remove the line, continue IV therapy, evaluate for metastatic foci (endocarditis, septic emboli)

B. Prosthetic Valve Endocarditis (PVE) - CoNS

• Rifampin penetrates biofilm and acts synergistically - do not use alone (resistance emerges rapidly)
• Gentamicin is given for the first 2 weeks only due to nephrotoxicity; monitor renal function
• In methicillin-susceptible strains: substitute nafcillin for vancomycin
• Surgical valve replacement is often required, especially when infection occurs at the valve-sewing ring (leads to dehiscence and mechanical failure)
• IV-to-oral step-down after ~2 weeks of successful IV therapy is increasingly supported by data for stable patients (Goldman-Cecil Medicine)

C. Native Valve Endocarditis (NVE) - CoNS (esp. S. lugdunensis)

• Vancomycin or nafcillin (based on susceptibility) for 4-6 weeks
• S. lugdunensis NVE: treat aggressively (similar to S. aureus) - penicillin/cefazolin if susceptible, vancomycin if resistant
• Surgical intervention often required given high rates of valvular destruction and embolic complications (Braunwald's Heart Disease)

D. CSF Shunt / CNS Device Infections

• Remove or externalize the infected device
• Vancomycin IV with or without intrathecal/intraventricular vancomycin in refractory cases
• Replace shunt after sterilization of CSF (typically after 7-10 days of negative cultures)
• Duration: typically 10-14 days after device removal

E. Prosthetic Joint Infections

• For device retention (DAIR - debridement, antibiotics, implant retention): IV vancomycin followed by oral rifampin + fluoroquinolone combination (e.g., rifampin + levofloxacin or ciprofloxacin)
• For device removal: IV vancomycin for 2-6 weeks
• Rifampin combination is the key to success when implant is retained - never use rifampin as monotherapy

F. UTI - S. saprophyticus

• Trimethoprim-sulfamethoxazole (TMP-SMX) x 3-7 days
• Nitrofurantoin x 5-7 days
• Fluoroquinolones (ciprofloxacin) as alternatives
• S. saprophyticus is typically methicillin-susceptible; beta-lactams also effective

Step 4: Biofilm and Device Management

• Physically protects bacteria from antibiotics and immune cells
• Anchors organisms to catheters, prosthetics, and synthetic polymers
• Is the primary reason device removal is often required for cure

"More than 50% of all infections of catheters and shunts are caused by coagulase-negative staphylococci."

• Medical Microbiology 9e

Step 5: Prevention

• Preoperative cefazolin prophylaxis for cardiac surgery, joint arthroplasty, vascular graft implantation
• When MRSA/MRSE colonization is likely: substitute vancomycin for cefazolin
• Strict sterile technique during catheter insertion; "catheter bundle" approach reduces CRBSI dramatically
• Chlorhexidine-impregnated dressings and antibiotic-impregnated catheters reduce colonization

Summary Table

• Red Book 2021, AAP - Coagulase-Negative Staphylococcal Infections, pp. 1073-1075
• Goldman-Cecil Medicine International Edition - Table 61-6 Definitive Therapy of Bacterial Endocarditis
• Medical Microbiology 9e - Staphylococcus epidermidis and Other Coagulase-Negative Staphylococci
• Braunwald's Heart Disease 15th Ed - Staphylococcal Species in IE
• Harrison's Principles of Internal Medicine 22E (2025) - Lipopeptides; IE management
• Katzung's Basic and Clinical Pharmacology 16th Ed - Clinical Uses (daptomycin, linezolid)