Ulcer or wound swabs

To diagnose wound infection, a combination of clinical assessment (see c_lwg2-c18-s2-1.html#lwg2-c18-s2-1__tlwg2-c18-tbl2), microbiological investigations, blood tests and imaging may be required. If indicated, collect wound swab for culture before starting antibiotic therapy. Indications for standard wound culture are:

wounds with overt signs and symptoms of infection, or signs of spreading or systemic infection (see c_lwg2-c18-s2-1.html#lwg2-c18-s2-1__tlwg2-c18-tbl2)
infected wounds that have failed to respond or are deteriorating, despite empirical antimicrobial treatment
for surveillance of drug-resistant bacteria as directed by local protocols
to determine appropriateness of surgery, if the presence of certain bacteria would prevent a surgical procedure (eg beta-haemolytic streptococci in wounds before skin grafting).

If a wound culture is indicated, the Levine technique is recommended. Wound culture enables accurate identification of pathogens and appropriate adjustment (ie de-escalation) of antibiotic therapy.

The Levine technique is:

cleanse and debride the wound (do not use antiseptic solutions)
moisten culture tip with sterile 0.9% sodium chloride (especially for dry wounds)
inform the patient that this procedure may cause discomfort
specimen should be obtained from the cleanest area of the wound (avoid slough or necrotic tissue)
firmly press swab tip into wound and rotate for 5 seconds (apply sufficient pressure so that tissue fluid is produced)
place swab into culture container using sterile technique
label container appropriately.

Consider the need for special stains or culture (eg mycobacterial or fungal organisms), and for Mycobacterium ulcerans polymerase chain reaction if Buruli ulcer is suspected. See Biopsy.

Once the swab is obtained, the sample should be immediately sent to the laboratory. Information to be provided with the specimen includes:

wound details (eg anatomical location, duration, aetiology)
patient details (eg demographics, significant comorbidities)
clinical indication for the swab (eg signs and symptoms, suspected pathogen)
current or recent antibiotic use.

If osteomyelitis is suspected, bone biopsy is recommended to identify deep wound pathogens; soft tissue or sinus tract specimens do not always predict pathogens in bone. For information about assessing patients for osteomyelitis, see Foot examination and Osteomyelitis.