How To Differentiate Between Infected Wounds And Colonized Wounds

Author(s): 
By Jason R. Hanft, DPM, and Brigette Smith, DPM

   Since every wound has the potential for infection, it is important to differentiate between infection and colonization.1 There is no textbook that depicts all the possible appearances of wounds that contain bacteria. Indeed, the potential of wounds to heal or become infected depends on many variables. Wound care specialists have a responsibility to become familiar with the these variables as well as develop a trained eye for the clinical appearance of a wound so they may render the appropriate treatment.

   There is an enormous amount of information concerning the treatment, staging and physiology of wounds and healing. The influx of emerging research is constantly affecting the current thinking on classifying wounds and providing appropriate treatment. Accordingly, one must be able to differentiate between contaminated and infected wounds, and understand how bioburden, critical colonization and the effects of bacteria affect the wound environment.

   The human body harbors over 200 species of bacteria on the skin.2 At any time, one of these bacteria can be inoculated into the wound. Once the skin is injured, the body is vulnerable to contamination from the environment, surrounding skin and mucous membranes.1 The longer the wound is exposed, especially if it is devitalized or compromised, the easier it is for bacteria to colonize.1

   In fact, wounds are an ideal place for bacteria to colonize and proliferate since they have a warm, moist nutritive environment. The type of bacteria present and whether the bacteria has infected the wound depends on the type, depth, location, level of perfusion and the efficacy of the host response.1 Consider the following equation relating to infection.3,4

Infection =
bacteria dose x virulence
host resistance

How Local And Systemic Factors Can Lead To Infection

   The interaction of bacteria with the host influences wound healing.3 Some vulnerabilities that can leave the host open to infection are age, obesity, malnutrition, chronic steroid use and immune defects. Systemic diseases such as diabetes and local issues such as venous hypertension are just some examples of the contributing factors that DPMs need to address at the initial assessment.

   Diabetes is a known factor in the host response, especially if the patient’s blood sugar is not well controlled. When the patient has uncontrolled blood sugar levels, there is evidence of a decrease in the function of polymorphonuclear cells that help with chemotaxis.4 Keeping the host defenses at peak efficiency can prevent infection in many cases.5

   Some local factors that affect a wound’s defense mechanisms are necrotic tissue, perfusion, foreign bodies, hematomas and dead space. If the tissue at the base or periphery of the wound is hypoxic, then fibrosis and/or necrosis will result. The longer bacteria are exposed to necrotic or fibrotic tissue, the more advantageous it is for the proliferation and colonization of bacteria.1

   The quality of perfusion of the wound is vital to healing. Microbial proliferation is greatly increased at PO26 It is beneficial to optimize tissue perfusion as this has a direct impact upon the ability of bacteria to proliferate. Demonstrating the positive impact of perfusion, one study showed anal wounds heal faster than lower extremity wounds due to the increased perfusion in the anal region. Despite the fact that the amount and type of bacteria are more difficult to control in this region, the anal wounds healed more rapidly.

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