WOUND SWAB

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Specimen: Pus in syringe or sterile container is preferable. Swab for Gram stain, swab in transport medium for culture. If fungal culture is required, it should be requested specifically.

Method: Gram stain for microscopy; culture on enriched, non-selective agar media and broth (eg cooked meat). Identification of significant isolates, then appropriate antibiotic sensitivity testing. Anaerobic culture in selected circumstances eg suspected actinomycosis.

Application: Investigation of an infected wound or lesion, when clinical assessment suggests that antibiotic or surgical drainage/debridement may be required. Investigation of wound infection as part of infection control measures, in hospitals or other institutions.

Interpretation: Pure growth of a single organism increases the likelihood that it is the pathogen. Recognised pathogens, eg Staphylococcus aureus, Streptococcus pyogenes, Clostridium perfringens, are specifically reported, even when there is a mixed growth. Antibiotic sensitivity tests are performed on recognised pathogens. Antibiotic treatment is appropriate for infection which is spreading, especially where systemic toxicity is present. The decision to treat a wound infection with antibiotics should be made on clinical grounds, not based on the results of a wound swab. For less serious wound infection, simple drainage may be sufficient.

Reference: Woods GL and Washington JA. In: Mandell GL et al eds. Principles and Practice of Infectious Diseases. 4th ed. Churchill Livingstone 1995.

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