How To Differentiate Between Infected Wounds And Colonized Wounds

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Continuing Education Course #132 — July 2005

I am pleased to introduce the latest article, “How To Differentiate Between Infected Wounds And Colonized Wounds,” in our CE series. This series, brought to you by the North American Center for Continuing Medical Education (NACCME), consists of regular CE activities that qualify for one continuing education contact hour (.1 CEU). Readers will not be required to pay a processing fee for this course.

As Jason R. Hanft, DPM, and Brigette Smith, DPM, point out, being able to distinguish between infected wounds and colonized wounds is no easy task. In an attempt to clarify this issue, they review the definition of these wounds, contributing factors to infected wounds and the impact of bioburden on wounds.

At the end of this article, you’ll find a 10-question exam. Please mark your responses on the enclosed postcard and return it to NACCME. This course will be posted on Podiatry Today’s Web site (www.podiatrytoday.com) roughly one month after the publication date. I hope this CE series contributes to your clinical skills.

Sincerely,

Jeff A. Hall
Executive Editor
Podiatry Today

INSTRUCTIONS: Physicians may receive one continuing education contact hour (.1 CEU) by reading the article on pg. 86 and successfully answering the questions on pg. 90. Use the enclosed card provided to submit your answers or log on to www.podiatrytoday.com and respond via fax to (610) 560-0502.
ACCREDITATION: NACCME is approved by the Council on Podiatric Medical Education as a sponsor of continuing education in podiatric medicine.
DESIGNATION: This activity is approved for 1 continuing education contact hour or .1 CEU.
DISCLOSURE POLICY: All faculty participating in Continuing Education programs sponsored by NACCME are expected to disclose to the audience any real or apparent conflicts of interest related to the content of their presentation.
DISCLOSURE STATEMENTS: Drs. Hanft and Smith have disclosed that they have no significant financial relationship with any organization that could be perceived as a real or apparent conflict of interest in the context of the subject of their presentation.
GRADING: Answers to the CE exam will be graded by NACCME. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam.
TARGET AUDIENCE: Podiatrists.
RELEASE DATE: July 2005.
EXPIRATION DATE: July 31, 2006.
LEARNING OBJECTIVES: At the conclusion of this activity, participants should be able to:
• cite contributing factors that may lead to infected wounds in the lower extremity;
• define colonization and infection;
• describe how wounds progress through the stages of wound healing;
• discuss the impact of bioburden on wound healing; and
• discuss clinical characteristics of mildly infected and moderately to severely infected wounds.

Sponsored by the North American Center for Continuing Medical Education.

Here is an example of a MRSA infection with accompanying cellulitis. (Photo courtesy of Lawrence Karlock, DPM)
Here is a necrotic infected heel ulcer with gangrenous changes. (Photo courtesy of Lawrence Karlock, DPM)
Here is an infected wound. Note the necrotic base with fibrosis. The wound borders are edematous with erythema extending > 2 cm. (Photo courtesy of Lawrence Karlock, DPM)
90
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 PO2 < 20 mmHg.6 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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