Investigation of surgical and non-surgical superficial skin and wound infections such as cellulitis, burns, bite wounds and ulcers (including pus, placental and penile swabs).
When the skin is broken as a result of trauma, burns, bites or surgical procedures, infection may occur. Common organisms causing skin and subcutaneous tissues infections include, Staphylococcus aureus and β haemolytic streptococci (S. pyogenes, S. dysgalactiae and S. agalactiae) in immunocompromised patients a broader range of organisms can cause disease.
Microbiological cultures may be undertaken to help establish the causative organism. This can be useful in cases where there is a wound to sample, especially when there is exudate. Swabs of intact skin should not be sent for culture. If there is pus present, it is generally more useful to collect the pus into a sterile universal, rather than sending a swab.
If there is a deep/chronic wound such as a chronic ulcer or surgical wound, it is often preferable to send deep tissue samples for culture, rather than surface swabs. Chronic wounds will become colonised with bacteria, some of which may not be causing infection. This makes the interpretation of surface swab results difficult and may cause inappropriate antibiotics use.
There are less common and rare skin and soft tissue infections of public health importance which should be considered in patients with specific risk factors such as:
- Panton-Valentine leucocidin (PVL) producing S. aureus in those in close contact accommodation, sharing laundering facilities (especially if laundering at <60°C), participating in close contact sports, and sharing towels
- Causes cellulitis, abscesses, boils and carbuncles, which are often recurrent.
- Cutaneous diphtheria in asylum seekers
- Often presenting as a chronic, nonhealing sores or shallow ulcers with a dirty gray membrane.
- Cutaneous anthrax in those who inject drugs or have animal contact
- Initially appears as a small, painless, pruritic papule which enlarges and develops a central vesicle or bulla. Which then erodes, leaving a painless necrotic ulcer with a black, depressed eschar
Sample the inflamed area/exudate using an appropriate swab and aseptic technique.
Best practice for swabbing ulcers and wounds
The diagnosis of infection is clinical and is likely to be present if the ulcer contains obvious purulent material (not just slough) or there is redness, swelling or warmth surrounding.
Cultures, although often requested, are frequently unhelpful and may only show colonizing organisms unless taken from the base after debridement. Instructions on how to take a swab properly can be found by visiting the Best Practice: Swabbing of Ulcers and Wounds for Bacterial Culture user guide.
- Specimens should be collected and transported in COPAN E-swabs.
- If sending pus, use a sterile white top universal.
- If cutaneous diphtheria or anthrax is suspected phone the laboratory to inform of the expected sample. There are additional safety precautions that are needed in the laboratory to process these samples.
Limitations and restrictions
- If processing is delayed, refrigeration at +2 to +8oC is preferable to ambient temperature.
- Delays over 48 hours are undesirable.
- Where possible samples should be taken prior to antibiotic therapy.
Microbiology Lab, James Cook University Hospital, Marton Road, TS4 3BW
Please see Bacteriology e-Swab user guide
Please provide all relevant clinical details to allow for optimal investigation of the sample.