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Test Taking Tip

Familiarize yourself with the following table for wound classifications and general indications for antibiotic therapy.


Name factors that influence the development of infection:

  • Poor approximation of tissue, hematoma/seroma, hypothermia, long operation (>2 hours), excessive local tissue destruction/necrotic tissue, low blood flow, foreign body, dead space, advanced age, chronic disease (e.g. COPD, renal failure, liver failure, diabetes mellitus), malnutrition, immunosuppressive drugs, and strangulation of tissues by tight sutures

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Wound Class Definition Infection Rate
Clean Nontraumatic, elective wound without acute inflammation 2%
Example: hernia
Clean-contaminated Wounds associated with operation on biliary, GU tract, or respiratory or GI tract without gross contamination 3%–5%
Example: elective colon resection with bowel prep
Contaminated Traumatic wound, GI tract spillage, acute inflammation, or a major break in sterile technique 5%–10%
Example: gunshot wound to colon with repair
Dirty Dirty traumatic wound, perforated viscous, or presence of pus 30%
Example: Abscess

Most common nosocomial infection:

  • Urinary tract infection (UTI)

How many colony-forming units (CFUs) are needed on urine culture to confirm a diagnosis of UTI?

  • >100,000 CFU

Most common nosocomial infection causing death:

  • Pneumonia

Overall most common organism in surgical wound infections:

  • Staphylococcus aureus

Most common anaerobe in surgical wound infections:

  • Bacteroides fragilis

When do wound infections classically arise?

  • Postoperative day 5 to 7

Treatment for a wound infection:

  • Remove sutures/staples, culture wound, examine to rule out fascial dehiscence, leave wound open and pack, start antibiotics

Bacteria that will cause wound infection and fever within 24 hours after surgery:

  • Group A β-hemolytic Streptococcus and Clostridium perfringens

Organisms that can cause necrotizing soft tissue infections:

  • Group A β-hemolytic Streptococcus, Clostridium perfringens, or mixed organisms

Usual organism to cause necrotizing fasciitis:

  • Beta-hemolytic group A Streptococcus or MRSA

Time period to wait before obtaining a CT scan to look for postoperative abscess:

  • >POD no. 7 (otherwise, abscess may look like normal post-op fluid collection)

Findings on CT scan to indicate abscess:

  • Gas in fluid collection, fibrous ring surrounding fluid collection

Usual initial treatment for intraabdominal abscess:

  • Percutaneous drainage and antibiotics

Most common bacteria to cause a line infection:

  • Staphylococcus epidermidis

How many CFUs are needed from ...

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