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  1. Cross, Heidi Huddleston MSN, RN, FNP-BC, CWOCN

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ONE OF THE BODY'S strongest defenses against infection is intact skin. After a break in the skin, the wound quickly becomes contaminated with organisms that predominate on the skin, such as Staphylococcus aureus. These Gram-positive organisms are generally followed by Gram-negative organisms such as Pseudomonas, E. coli, Klebsiella, and Proteus. Later, anaerobic organisms and fungi join the fray.1


If bacteria continue to proliferate, the wound moves through the stages of bacterial bioburden, ranging from contamination to colonization to critical colonization to actual infection. Wound infection is defined as a quantitative bacterial count of 105 colonies of bacteria (greater than or equal to 105 colony-forming units [CFUs]/gram of tissue or mL wound fluid).2 (See The burdening stages of bioburden.)


Keep in mind that every wound is contaminated, so a positive culture doesn't necessarily indicate infection. This must be clinically determined based on wound characteristics and signs and symptoms of infection such as erythema, edema, pain, heat, and increased exudate and odor. Culture and sensitivity testing shows the type of bacteria in the wound and guides antimicrobial therapy.


Specimens for culture and sensitivity testing can be obtained by tissue biopsy, needle aspiration, or swab. Although tissue biopsy is considered the gold standard, swab specimens are more commonly used because they're most easily collected and readily available.2 This article reviews the current best practice for obtaining a swab specimen for wound culture.


Ten steps to success

Using proper technique to obtain a swab specimen is vital to avoid false-negatives and false positives in a wound culture, which may result in either overtreatment or undertreatment with antimicrobials. The Z technique (rotating the swab in a zigzag fashion covering the entire injured area across the wound, without touching the wound edges) is no longer recommended (63% sensitivity, 53% specificity).3 Current best practice calls for the Levine technique (91% sensitivity, 57% specificity).1,4-6 (See Using the Levine technique.) Follow these steps to obtain a specimen with the Levine technique:1,6


1. If possible, obtain the specimen before the patient starts antimicrobial therapy, which interferes with microorganism growth.7


2. Assemble all equipment: unsterile gloves, 10-mL syringe prefilled with 0.9% sodium chloride, sterile gauze pads, culture swab, sterile swab container, and the appropriate wound dressing. Even though a 35 cc syringe with a 19 gauge angiocath is recommended for optimally cleansing the wound, this may be hard to come by. So using a 10-mL syringe with 0.9% sodium chloride (which is more readily available) is sufficient for flushing away wound debris before obtaining the culture.8


3. After performing hand hygiene and putting on unsterile gloves irrigate the wound with 0.9% sodium chloride and wipe gently with the gauze pad.


4. Moisten the swab with 0.9% sodium chloride (a moist swab provides more accurate data than a dry swab).


5. Identify a small area (1 cm2) of clean viable tissue and rotate the swab on it, avoiding any necrotic tissue. Applying pressure, try to express as much nonpurulent wound fluid as possible. A wound culture must be taken from clean tissue because pus or necrotic tissue will not provide an accurate profile of the microflora contained within the tissue.


6. Insert swab into the sterile container.


7. Redress the wound and perform hand hygiene.


8. Assess the patient and ensure that any wound pain has been managed. (This is done initially and again during the process.)


9. Complete the lab slip and/or electronic document, including wound site, time the specimen was collected, and any antimicrobials the patient is receiving.


10. Send the specimen to the lab immediately (within 1 hour) to keep the specimen stable.1



Closely follow these 10 steps whenever obtaining a swab specimen to ensure patient safety and successful antimicrobial therapy.

Table The burdening ... - Click to enlarge in new windowTable The burdening stages of bioburden
Figure. Using the Le... - Click to enlarge in new windowFigure. Using the Levin technique



1. Stotts N. Wound infection: diagnosis and management. In: Bryant R, Nix D, eds. Acute and Chronic Wounds: Current Management Concepts. St. Louis, MO: Elsevier Mosby; 2012:270-278. [Context Link]


2. Wounds International. Infection update. 2012. http://www.woundsinternational.com/pdf/content_10386.pdf. [Context Link]


3. Rondas AA, Schols JM, Halfens RJ, Stobberingh EE. Swab versus biopsy for the diagnosis of chronic infected wounds. Adv Skin Wound Care. 2013;26(5):211-219. [Context Link]


4. Gardner SE, Frantz RA, Saltzman CL, Hillis SL, Park H, Scherubel M. Diagnostic validity of three swab techniques for identifying chronic wound infection. Wound Repair Regen. 2006;14(5):548-557. [Context Link]


5. Cooper R. Ten top tips for taking a wound swab. 2010. http://www.woundsinternational.com/practice-development/ten-top-tips-for-taking-. [Context Link]


6. Bonham PA. Swab cultures for diagnosing wound infections: a literature review and clinical guideline. J Wound Ostomy Continence Nurs. 2009;36(4):389-395. [Context Link]


7. Centers for Disease Control and Prevention. Clinician guide: get smart for healthcare. 2012. http://www.cdc.gov/getsmart/healthcare/implementation.html. [Context Link]


8. Gabriel A.Wound irrigation. 2013. http://emedicine.medscape.com/article/1895071-overview. [Context Link]