What is the most common source of surgical site infection, the patient or the hospital?

Most Common Source of Surgical Site Infection

The most common source of surgical site infection is the patient's own endogenous flora, particularly in clean-contaminated or contaminated procedures, while Staphylococcus aureus from the patient's skin flora or the exogenous environment is the predominant cause in clean surgical procedures. 1

Patient-Related Sources of Surgical Site Infections

• In clean surgical procedures (where gastrointestinal, gynecologic, and respiratory tracts are not entered), Staphylococcus aureus from the patient's skin flora is the most common cause of surgical site infection 1, 2
• In clean-contaminated or contaminated surgical procedures, the aerobic and anaerobic pathogens of the patient's normal endogenous microflora from the surgically resected organ are the most frequently isolated pathogens 1
• Infections of contaminated operations involving perioral, perirectal, and vulvovaginal tissues yield bacteria similar to the normal microbial flora of the adjacent mucous membrane 1
• The patient's own skin flora, including S. aureus, coagulase-negative staphylococci, Propionibacterium acnes, and diphtheroids, are responsible for most surgical site infections 3

Hospital or Environmental Sources

• In clean surgical procedures, Staphylococcus aureus from the exogenous environment can also be a cause of infection, though less common than the patient's own flora 1
• For patients hospitalized longer than 5-7 days, exogenous and hospital flora gain advantage and become more likely sources of infection 4
• Hospital-acquired pathogens, particularly MRSA, are associated with specific risk factors including: patients from long-stay care facilities, hospitalization within the preceding 30 days, prior antibiotic therapy, and prolonged current hospitalization 1

Pathogen Distribution by Surgical Site

• In trunk and extremity surgeries away from axilla or perineum, Staphylococcus aureus predominates 1
• In axilla or perineum surgeries, mixed flora including skin organisms and enteric bacteria are common 1
• In gastrointestinal tract surgeries, Escherichia coli is the most prevalent microorganism (47.8%), followed by Enterococcus fecalis (13.0%) and Pseudomonas aeruginosa in combination with E. coli (13.0%) 5

Host Factors Contributing to Infection Risk

• Patient-related factors significantly impact the risk of surgical site infections, including:
  • Age, malnutrition status, diabetes, smoking, and obesity 1, 6
  • Colonization with microorganisms, particularly MRSA 1
  • Length of hospital stay or previous hospitalization 1
  • Shock, hypoxemia, and hypothermia 1
  • Immunosuppression and malignancies 1

Surgical Factors Affecting Infection Risk

• Degree of wound contamination (clean, clean-contaminated, contaminated, or dirty) 2
• Duration of operation, with longer procedures increasing risk 1, 5
• Intraoperative blood loss and hypotension 5
• Emergency versus elective surgery 1
• Proper administration of antimicrobial prophylaxis 1

Clinical Implications

• Understanding the source of surgical site infections helps guide appropriate preventive measures and treatment strategies 2
• Proper skin antisepsis before surgery is crucial, with chlorhexidine-alcohol solutions showing higher efficacy than povidone-iodine 4
• Antibiotic prophylaxis should be targeted to the most likely pathogens based on the surgical site and procedure type 1
• For clean procedures, coverage should focus on gram-positive organisms, particularly S. aureus 1
• For procedures involving the gastrointestinal tract, perineum, or female genital tract, broader coverage including gram-negative bacteria and anaerobes is necessary 1

Common Pitfalls in Management

• Failing to recognize that the patient's own flora is the predominant source of infection can lead to inappropriate preventive measures 1
• Overuse of broad-spectrum antibiotics when narrow-spectrum would be appropriate for clean procedures 1
• Continuing antibiotics beyond 24-48 hours postoperatively provides no additional benefit and increases risk of resistance 1
• Neglecting to inspect surgical wounds daily for signs of infection 1
• Culturing wounds without clinical signs of infection is not recommended and may lead to unnecessary treatment 1

Understanding that the patient's own flora is the primary source of surgical site infections should guide infection prevention strategies, with particular attention to proper skin preparation, appropriate antibiotic prophylaxis, and meticulous surgical technique.