Surgical Site Infection: Diagnosis and Management
Definition and Diagnostic Criteria
A postoperative wound should be considered a surgical site infection when it occurs within 30 days of surgery and meets specific diagnostic criteria based on anatomical depth. 1
Superficial Incisional SSI
- Involves only skin and subcutaneous tissue above the fascia 1
- Requires at least one of the following: 1
- Purulent drainage from the incision
- Positive culture from aseptically obtained fluid or tissue
- Local signs (pain, tenderness, swelling, erythema) after surgeon opens the incision
- Diagnosis by the attending surgeon based on clinical judgment
Deep Incisional SSI
- Involves fascia and muscle layers 1, 2
- Occurs within 30 days (or up to 1 year with implants) 1, 2
- Requires purulence, dehiscence, abscess on reoperation/imaging, or clinical diagnosis 1
- Associated with 13.2% mortality and 53.2% reoperation rate 2
Organ/Space SSI
- Involves organs or spaces opened during surgery (excluding the incision itself) 1, 2
- Same timeframe as deep infections 1
- Mortality rate of 5.7% with 44.0% requiring reoperation 2
Critical pitfall: SSIs rarely occur within the first 48 hours postoperatively; fever during this period is usually non-infectious unless caused by Streptococcus pyogenes or Clostridium species. 1, 2
Management Algorithm
Step 1: Assess for Systemic Inflammatory Response
Determine whether systemic signs are present, as this dictates whether antibiotics are needed in addition to surgical management. 1, 2
- Erythema/induration extending >5 cm from wound edge
- Temperature >38.5°C
- Heart rate >110 beats/minute
- White blood cell count >12,000/µL
Step 2: Primary Surgical Management
Suture removal plus incision and drainage is the cornerstone of SSI treatment and must be performed first. 1, 2
- Remove sutures and open the wound widely 1
- Evacuate all purulent material and break up loculations 3
- Obtain Gram stain and culture before starting antibiotics 2, 3
- Cover with dry sterile dressing (avoid packing with gauze as it increases pain without improving healing) 3
Step 3: Determine Need for Antibiotics
Antibiotics are NOT routinely required after adequate drainage unless systemic signs are present. 1, 2
Antibiotics NOT Needed:
- Superficial SSI with adequate drainage and no systemic signs 1, 2
- Local wound care alone is sufficient in approximately 73% of superficial SSI 4
Antibiotics ARE Needed:
- Any systemic inflammatory response criteria present 1, 2
- Deep incisional or organ/space infections (require antibiotics in 100% of cases) 2
- Immunocompromised patients 1, 3
- Signs of organ failure (hypotension, oliguria, altered mental status) 1
Empiric Antibiotic Selection
For Clean Operations (Trunk, Head/Neck, Extremities)
The primary pathogens are staphylococci, so coverage should target MSSA or MRSA based on risk factors. 1
Standard Risk (MSSA Coverage):
- First-generation cephalosporin (e.g., cefazolin) OR 1
- Antistaphylococcal penicillin (e.g., nafcillin, oxacillin) 1
High MRSA Risk:
Use MRSA-active agents when the following risk factors are present: 1
- Nasal MRSA colonization
- Prior MRSA infection
- Recent hospitalization
- Recent antibiotic exposure (especially beta-lactams, carbapenems, or quinolones within 30 days) 1
- Age ≥75 years 1
- Long-term care facility residence 1
- Charlson score >5 1
- Current hospitalization >16 days 1
MRSA-active options: 1
- Vancomycin (first-line)
- Linezolid
- Daptomycin
- Telavancin
- Ceftaroline
For Operations on Axilla, GI Tract, Perineum, or Female Genital Tract
These sites require coverage for gram-negative bacteria AND anaerobes in addition to staphylococci. 1
Standard Regimens:
For Severe/Deep Infections:
- Piperacillin-tazobactam OR 2
- Carbapenem (meropenem, imipenem) 2
- Add MRSA coverage (vancomycin, linezolid, or daptomycin) if risk factors present 2
Beta-Lactam Allergy Alternatives
For patients with true type 1 hypersensitivity (anaphylaxis or urticaria) to beta-lactams, use non-beta-lactam alternatives. 3
For MSSA Coverage:
For MRSA Coverage:
For Gram-Negative/Anaerobic Coverage:
- Fluoroquinolone (ciprofloxacin or levofloxacin) + metronidazole 1
- Aztreonam + metronidazole (aztreonam has no cross-reactivity with beta-lactams)
Important caveat: Cephalosporins have <3% cross-reactivity with penicillins in true IgE-mediated allergy, so first-generation cephalosporins may be used cautiously in patients with non-severe penicillin allergy (rash only), but should be avoided in anaphylaxis. 3
Duration of Antibiotic Therapy
Antibiotic duration should be brief and guided by clinical response, not arbitrary fixed courses. 1, 2, 4
- Superficial SSI with systemic signs: 5-10 days (average 19.6 days in practice) 3, 4
- Deep SSI: Average 40.8 days, but individualize based on clinical improvement 4
- After adequate drainage: Continue only until systemic signs resolve (typically 24-48 hours) 2
- Organ/space infections: Prolonged therapy often required, guided by source control and clinical response 2
Critical pitfall: Continuing antibiotics beyond 48 hours after clinical improvement following adequate drainage is discouraged and promotes resistance. 2
Special Considerations
Pseudomonas Risk
Consider anti-pseudomonal coverage for surgeries involving the axilla, GI tract, perineum, or in patients with diabetes, prior antibiotic use, or known colonization. 5
- Hospital water systems and tap water used for equipment rinsing are primary reservoirs 5
- Use sterile water (not tap water) for terminal rinsing of surgical equipment 5
Instrumentation/Implants
Retain instrumentation whenever possible; exchange only if loose. 4
- Single-stage debridement with retention is effective in 76% of deep SSI with hardware 4
- Deep SSI with prosthetic implants caused by MRSA, Pseudomonas, or multidrug-resistant organisms have poorer prognosis 5
Culture Results
Always obtain cultures before starting antibiotics to allow de-escalation based on susceptibilities. 2, 3