A microbiologist's view of factors contributing to infection

Why some patients develop postoperative surgical wound infection and others do not remains a mystery. There are many risk factors for infection, and mathematical scoring systems are often good predictors of infection; yet, some patients with a plethora of risk factors fail to develop surgical site infections. Even patients with established abdominal infection do not automatically develop wound infection. Early experimental work, now confirmed in the clinical setting, dictates that bacteria must be in the wound to cause infection; the minimal infecting dose will depend on the environmental conditions in the wound. The presence of foreign bodies, trauma, hematoma, etc., will enhance the effect of the inoculum; therefore, surgical debridement and careful surgery are necessary to reinforce the host defenses. Some bacteria, e.g., Staphylococcus aureus and Streptococcus pyogenes, have a greater propensity to cause infection, so extensive infection-control practices are necessary to prevent or contain these pathogens. To minimize the risk of surgical site infection, individual patient risk factors must be identified and modified whenever possible. The patient should be prepared for the operation and appropriate skin antiseptics should be used on the operative site. The patient should be considered for perioperative antibiotic prophylaxis and, if appropriate, bowel preparation should be carried out. Care and attention to the theater operating environment is important, especially for cases in which airborne transmission of bacteria should be controlled, e.g., ultraclean air systems for implant surgery. In elective surgery, the source of bacteria that cause infection is either the patient's normal flora (e.g., skin or bowel), i.e., endogenous, or the surgical staff or environment, i.e., exogenous. Surgical expertise and theater discipline are essential components in the fight against surgical sepsis.