What are the diagnosis and treatment options for surgical site infections?

Surgical Site Infection: Diagnosis and Treatment

Surgical site infections (SSIs) require prompt diagnosis through clinical evaluation and appropriate cultures, followed by incision and drainage as primary treatment, with adjunctive antibiotics reserved for cases with systemic signs of infection or high-risk anatomical locations. 1

Diagnosis of Surgical Site Infections

Classification of SSIs

SSIs are categorized into three types based on anatomical involvement:

1. Superficial incisional SSI:

   • Occurs within 30 days of surgery
   • Involves only skin/subcutaneous tissue
   • Diagnostic criteria: purulent drainage, positive cultures from aseptically collected fluid/tissue, local signs of infection, or diagnosis by attending clinician 1

2. Deep incisional SSI:

   • Occurs within 30 days, or up to 1 year if implant present
   • Involves fascia and deep muscle layers
   • Diagnostic criteria: purulent drainage, deep incision dehiscence, abscess found during reoperation, radiologic/histologic evidence, or diagnosis by attending clinician 1

3. Organ/space SSI:

   • Occurs within 30 days, or up to 1 year if implant present
   • Involves any part of body opened/manipulated during surgery other than the incision
   • Diagnostic criteria: purulent drainage from drain, positive cultures from aseptically collected fluid/tissue, abscess found during reoperation, or diagnosis by attending clinician 1

Diagnostic Approach

1. Clinical assessment:

   • Purulent drainage (diagnostic of SSI)
   • Spreading inflammation exceeding normal healing
   • Pain, tenderness, swelling, erythema
   • Timing: Early infections (<48 hours) suggest virulent organisms like β-hemolytic streptococci or Clostridium; most SSIs appear between 4-6 days postoperatively 1

2. Microbiological diagnosis:

   • Obtain wound swabs when purulence or spreading cellulitis present 1
   • Culture of aseptically collected deep fluid/tissue is diagnostic of infection
   • Growth of >10^5 bacteria per gram of tissue is considered diagnostic 1
   • Two sets of blood cultures should be obtained in cases of deep SSI with systemic signs 1

3. Imaging:

   • Ultrasound is first-line for detecting deep collections
   • CT scan when ultrasound is not diagnostic 1

Treatment of Surgical Site Infections

Primary Treatment

1. Incision and drainage:

   • Suture removal plus incision and drainage is the primary treatment for SSIs 1
   • All infected wounds should be opened 1

2. Wound management:

   • Appropriate dressing changes after drainage
   • For superficial infections without systemic signs, dressing changes alone may be sufficient 1

Antibiotic Therapy

1. Indications for antibiotics:

   • Not routinely indicated for all SSIs 1
   • Beneficial for SSIs with significant systemic response:
     • Erythema/induration extending >5 cm from wound edge
     • Temperature >38.5°C
     • Heart rate >110 beats/minute
     • WBC count >12,000/μL 1
   • Brief course indicated for infections following clean operations with systemic signs 1

2. Antibiotic selection based on surgical site:

   • Clean operations on trunk, head/neck, extremities:

     • First-generation cephalosporin (e.g., cefazolin) for MSSA 2
     • Vancomycin, linezolid, daptomycin, or telavancin for suspected MRSA (risk factors: nasal colonization, prior MRSA infection, recent hospitalization, recent antibiotics) 1

   • Operations on axilla, GI tract, perineum, female genital tract:

     • Agents covering gram-negative bacteria and anaerobes:
       • Cephalosporin + metronidazole 3
       • Fluoroquinolone + metronidazole 1
       • Carbapenem monotherapy 1

3. Special considerations:

   • For contaminated or dirty abdominal wounds, assume anaerobic coinfection even if not identified by routine microbiology 1
   • When deep SSI or intra-abdominal sepsis is present, polymicrobial infection is common, and blood cultures may not identify all organisms, particularly anaerobes 1

Risk Stratification and Prevention

Risk Assessment

Wound categories correlate with infection rates:

1. Clean: 1.5% infection rate
2. Clean-contaminated: 7.7% infection rate
3. Contaminated: 15.2% infection rate
4. Dirty: 40% infection rate 1

Prevention Strategies

1. Preoperative:

   • Avoid razors for hair removal (use clippers instead) 4
   • Decolonization with intranasal antistaphylococcal agents and skin antiseptics for high-risk procedures 4
   • Chlorhexidine gluconate plus alcohol-based skin preparation 4

2. Intraoperative:

   • Maintain normothermia (>36°C) using active warming 4
   • Perioperative glycemic control (glucose <150 mg/dL) 4

3. Postoperative:

   • Consider negative pressure wound therapy for high-risk wounds 4

Common Pitfalls and Caveats

1. Diagnostic challenges:

   • Qualitative culture of wound swabs has limited value due to inevitable contamination of open wounds 1
   • Detection of anaerobic organisms requires specific collection and transport methods 1

2. Treatment pitfalls:

   • Overuse of antibiotics for superficial SSIs without systemic signs
   • Failure to recognize early infections (<48 hours) which may indicate highly virulent organisms requiring urgent treatment 1
   • Inadequate drainage of deep collections

3. Special populations:

   • SSIs with implanted prosthetic material require longer surveillance (up to 1 year) and may need extended antibiotic therapy 1
   • Immunocompromised patients may present with atypical or subtle signs of infection

By following this systematic approach to diagnosis and treatment, clinicians can effectively manage surgical site infections while minimizing morbidity and mortality.