Taking a wound swab
The principles of specimen collection are set out in Chapter 51. A wound swab is required if there is a clinical suspicion that infection is present. ‘Just in case’ wound swabs are not helpful and the midwife should be confident that clinical signs of infection are present – this includes redness, heat, pain and the presence of pus. If a discharge is present from the wound the following should be recorded:
- Presence of pus.
Wound swabs should be collected and sent to the laboratory in a timely way for culture and sensitivity testing.
Indications include infected surgical wounds, for example perineum, umbilicus, and invasive device insertion site (e.g. central line insertion site, drain site, suprapubic catheter site). Infected chicken pox pustules would also meet the definition of a wound.
The midwife should:
- Correctly complete the laboratory request form.
- Gain patient consent to take the specimen and inform the patient of the rationale for it.
- Ensure the patient is comfortable, and their privacy and dignity is maintained.
- Collect the specimen in a way that avoids contamination – see Chapter 5 (Asepsis and sepsis).
- Use the correct transport medium.
- Arrange transportation to the laboratory in a timely way or store appropriately if necessary.
- Check and act on results once they are available.
- Document collection of the specimen and the results together with any resulting actions.
Once the swab has been obtained it should be placed in a plastic specimen bag together with the laboratory form in line with local policies and procedures. Specimens should be sent to the laboratory as soon as possible and should not be left for long periods at ambient temperatures as this may result in overgrowth of commensal bacteria, which can impact on the accuracy of the laboratory result.
If transport to the laboratory will be delayed the specimen should be refrigerated (not in a food fridge) until the next available laboratory collection.
Note: this procedure requires an aseptic technique to avoid contamination of the swab or wound, which could lead to incorrect laboratory analysis due to contamination of equipment or the specimen.
- Positively identify the patient.
- Ensure all necessary equipment is available (including correct swab and laboratory form).
- Explain the procedure to the patient.
- Obtain patient consent.
- Obtain the swab before antibiotics are commenced wherever possible.
- Perform hand hygiene before patient contact.
- Remove old wound dressing if present – use personal protective equipment (PPE – gloves and apron) if required.
- Dip swab in transport media included in swab container or moisten with sterile saline (do not use tap water) (Figures 52.1).
- Rotate the swab over the area to be swabbed using a zig zag motion, ensuring you make contact with the area of the wound showing signs of infection (Figure 52.2).
- If a wound sinus is suspected or present do not probe the tract as exploration of the sinus should only be undertaken with a dedicated sinus probe. Cotton tips/ swabs or applicators should not be used for exploration. Swabbing of the sinus, if requested, should be undertaken by or with the support of tissue viability or surgical specialists.
- If pus is present swab pus.
- Replace swab in the container (Figure 52.3).
- Redress wound if necessary.
- Remove PPE and perform hand hygiene.
- Make the woman comfortable.
- Complete patient identification labels and send to laboratory.
Document in patient records.
Pus usually presents as a white/yellowish discharge. It comprises dead leucocytes, which are produced by the body in response to the presence of infection.
Large wounds may include chronic wounds. In the maternity setting chronic wounds may include pressure ulcers or diabetic foot wounds. Large wounds may include areas of debridement (for example following breakdown of a caesarean section wound) or burns. It is not possible or necessary to swab the whole wound – attention should be paid to areas where inflammation or exudate/ pus are present.
Chronic wounds, as described above, are often heavily colonised with bacteria and do not require regular or ‘just in case’ swabbing. Swabs should only be taken if the presence of infection is suspected. In chronic wounds infection is characterised by increasing pain, inflammation/cellulitis and a pyrexia. If a sample of the wound is required, a tissue biopsy rather a wound swab is the preferred microbiological sample.
If a swab is required:
- Cleanse the wound by irrigating with sterile/tap water or saline to remove surface bacterial contaminants in line with local policies.
- Remove any slough and necrotic tissue if easily dislodged.
- Swab viable wound tissue only (do not take swabs from necrotic areas) on the edge of the wound or from areas showing signs of infection.
For complex wounds the expertise of tissue viability specialists should be sought.