Chapter 8

### Surgical Infections

A surgical infection is an infection that (1) is unlikely to respond to nonsurgical treatment (it usually must be excised or drained) and occupies an unvascularized space in tissue or (2) occurs in an operated site. Common examples of the first group are appendicitis, empyema, gas gangrene, and most abscesses.

Surgeons are regrettably familiar with the vicious circle of operation or injury, infection, malnutrition, immunosuppression, organ failure, reoperation, further malnutrition, and further infection. One of the fine arts of surgery is to know when to intervene with excision, drainage, physiologic support, antibiotic therapy, and nutritional therapy. For infections arising in a space or in dead tissue, by far the most important aspect of treatment is to establish surgical drainage.

#### Pathogenesis

Three elements are common to surgical infections: (1) an infectious agent, (2) a susceptible host, and (3) a closed, unperfused space.

##### The Infectious Agent

Although a few pathogens cause most surgical infections, many organisms are capable of doing so. Among the aerobic organisms, streptococci may invade even minor breaks in the skin and spread through connective tissue planes and lymphatics. Staphylococcus aureus is the most common pathogen in wound infections and around foreign bodies. Klebsiella often invades the inner ear and enteric tissues as well as the lung. Enteric organisms, especially the Enterobacteriaceae and enterococci, are often found together with anaerobes. Among the anaerobes, bacteroides species and Peptostreptococci are often present in surgical infections, and clostridium species are major pathogens in ischemic tissue.

Pseudomonas and serratia are usually nonpathogenic surface contaminants but may be opportunistic and even lethal invaders in critically ill or immunosuppressed patients. Some fungi (histoplasma, coccidioides) and yeasts (candida), along with nocardia and actinomyces, cause abscesses and sinus tracts, and even animal parasites (amebas and echinococcus) may cause abscesses, especially in the liver. Destructive granulomas, such as tuberculosis, once required excision, but antibiotic therapy has now superseded operation for this purpose in most cases. Other rare diseases such as cat-scratch fever, psittacosis, and tularemia may cause suppurative lymphadenitis and require drainage or excision.

Identification of the pathogen by smear and culture remains a cardinal step in therapeutic decision making. The surgeon must inform the microbiologist of peculiar circumstances associated with any given specimen, so that appropriate smears and cultures can be done; serious errors may otherwise result.

##### The Susceptible Host

Surgical infections such as appendicitis and furuncles occur in patients whose only defect in immunity is a closed space in tissue. However, patients with suppressed immune systems are being seen with increasing frequency, and their problems have become a major surgical challenge. Immunosuppression seems a simple concept but in fact usually represents a combination of defects of the multifaceted immune mechanism.

###### Specific Immunity

The immune process that depends upon prior exposure ...

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