General Considerations
- Preferably collect specimen prior to institution of therapy and only from wounds that have clear signs of clinical infection, are deteriorating, or that fail to heal over a long period. Indiscriminate submission of a wound specimen, especially from a superficial site, may provide useless information that leads to unnecessary antibiotic treatment.
- Always cleanse/debride the skin or mucosal surface to be sampled. Do not skip this step. Proper preparation of the wound can minimize contamination.
- Sample viable tissue rather than superficial debris.
- Obtain aspirates or biopsy samples rather than swabs. Note, however, that because of variability in numbers and types of organisms present in different parts of chronic wounds, the validity and value of a single biopsy specimen is debatable.
- Gram stain will be done on specimens of sufficient quantity, even if it is not ordered. Note: if specimens are collected on swabs, always submit two (see below). The quality of the specimen and determination of extent of workup will be based on Gram stain results. The presence of epithelial cells indicates contamination of the specimen with skin or mucous membrane microbiota while the presence of leukocytes is a good indicator of infection.
- Information regarding the type of wound (surgical, traumatic pressure ulcer etc.) and location of the wound is important and should be indicated when ordered.
- Tissues and aspirates are acceptable for anaerobic culture, if indicated.
Closed abscesses
Disinfect as for blood culture collection. Aspirate infected material with needle and syringe. If the initial aspiration fails to obtain material, inject sterile nonbacteriostatic saline subcutaneously and repeat the aspiration attempt. Place contents into a sterile tube for submission to the laboratory.
Fine needle aspiration
Disinfect as for blood culture collection. Insert the needle into the tissue, using various directions, if possible. If the volume of aspirate is large, place the contents into a sterile tube for submission to the laboratory. If the volume of aspirate is small, draw up a small amount of sterile nonbacteriostatic saline and draw up and down to release the specimen from the syringe into the sterile tube. Note: Needle aspirates may result in underestimation of bacterial isolates compared to more accurate deep biopsy specimens.
For anaerobic culture, if appropriate, place the tissue in an anaerobic transport tube.
Open Wounds
Cleanse the wound margins and superficial area thoroughly with sterile saline, changing sponges with each application. Remove all superficial exudates. Remove overlying debris with a scalpel and swabs or sponges. Collect a biopsy or curette sample from the base or advancing margin of the lesion. Collect sufficient tissue (3-4mm biopsy samples), avoiding necrotic areas. For aerobic culture, place tissue in a sterile container with a small amount of nonbacteriostatic saline (just enough to keep the specimen from drying out). For anaerobic culture, if appropriate, place the tissue in an anaerobic transport tube.
Pus
Aspirate the deepest portion of the lesion or exudate with a syringe and needle. Submit pus in a sterile tube. Also collect a biopsy sample of the advancing margin or base of the infected lesion after excision and drainage (see above). For infected bite wounds, aspirate pus from the wound, or obtain it at the time of incision and drainage. Do not culture fresh bite wounds. They will harbor resident respiratory flora introduced from the bite but cultures cannot predict if they will cause infection. Anaerobic culture is not appropriate.
Swabs
Collect swabs only when tissue or aspirate cannot be obtained. Always submit two swabs so that Gram stain can be performed. Workup is based on the number of inflammatory cells, epithelial cells and organisms seen on Gram stain. Limit swab sampling to wounds that are clinically infected or those that are chronic and are not healing. To minimize contamination, it is important to cleanse the wound to remove superficial debris by thorough irrigation and cleansing with nonbacteriostatic sterile saline. If the wound is relatively dry, collect the specimen with two cotton-tipped swabs moistened with sterile non-bacteriostatic saline. Gently roll the swab over the surface of the wound approximately five times, focusing on an area where there is evidence of pus or inflamed tissue. Anaerobic culture is not appropriate. |
