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Venous leg ulcers: infection diagnosis and microbiological investigation

Background

  • A venous leg ulcer is defined as 'the loss of skin below the knee on the leg or foot, which takes more than 6 weeks to heal'
  • An assessment should be carried out by a healthcare professional trained in leg ulcer management. This should include clinical history; Doppler studies to exclude arterial insufficiency; assessment of pain, odour, and discharge; oedema; venous eczema and infection; assessment of risk factors and comorbidities
  • If a leg ulcer is associated with signs of venous hypertension (e.g. varicose veins), NICE recommends referral to a vascular service
  • Ulcerated legs should be washed normally in tap water and carefully dried with a smooth, soft material. Management includes cleaning, debriding, and dressing the ulcer; applying compression therapy if the ulcer is not infected; arranging a follow-up to assess the ulcer

Microbiology and venous leg ulcers

  • Routine bacteriological samples should not be taken. Treat the patient not the culture results
  • All venous leg ulcers contain bacteria. Most bacteria are colonisers; only in some instances does clinical infection occur
  • In patients with chronic venous leg ulcers, only use systemic antibiotics if there is evidence of clinical infection
  • Do not use antibiotics routinely in venous leg ulcers. Overuse of antibiotics will select for resistant organisms

When should I take a microbiological sample from a venous leg ulcer?

  • If there are any of the following criteria that indicate the presence of infection:
    • increased odour or increased exudate from the ulcer
    • enlarging ulcer with abnormal bleeding or bridging granulation tissue
    • increased disproportionate pain
    • cellulitis (particularly if spreading), lymphangitis, or lymphadenopathy
    • pyrexia, systemic inflammatory response syndrome, or sepsis
  • Samples should always be collected before antibiotics are started
  • Only patients with a non-healing or atypical venous leg ulcer should be referred for consideration of biopsy

How should I take a microbiological swab from a venous leg ulcer?

  • Use a swab with charcoal transport medium
  • Cleanse the wound with tap water or saline to remove surface contaminants, slough, and necrotic tissue
  • Swab viable tissue that displays signs of infection, whilst rotating the swab. Alternatively, use the Levine technique in which the swab is pressed into the ulcer bed, as this displaces deeper placed organisms
  • Send the swab to the microbiology laboratory as soon as possible to aid survival of fastidious organisms
  • For all specimens include all clinical details (patient details, site, nature of wound, and current or recent treatment), to enable accurate processing and reporting of the specimen

Interpreting the laboratory report

  • The result will only provide information about the organisms present and their antibiotic susceptibilities. The results will not tell you if infection is present in a venous leg ulcer, as this is a clinical diagnosis
  • All venous leg ulcers are colonised by bacteria, which may progress to a level of so-called 'critical colonisation'. Above this, healing is delayed and significant infection occurs. No simple test can differentiate colonisation from infection. Early colonisation of venous leg ulcers is not considered adverse to healing
  • Group A β-haemolytic streptococci can be associated with significant infection and delayed healing. When diagnosed, these infections justify early, aggressive, systemic antimicrobial therapy
  • Other streptococci, Staphylococcus aureus, and anaerobes may be associated with clinical infection. Most other bacterial colonisation of wounds is not considered to adversely affect healing
  • Treatment to be based on signs of infection, as inclusion of antibiotic susceptibilities on the report does not mean that an organism is significant or that it requires antibiotics

When should I use antiseptics or antibiotics in venous leg ulcers?

  • Topical antiseptics may be of benefit to individual patients, but are not routinely recommended in the treatment of venous leg ulcers. Some evidence supports the use of cadexomer iodine for critically colonised ulcers or early infection, but further research is required before recommendations can be made about other agents
  • Systemic antibiotics are indicated in the presence of locally spreading cellulitis or other signs of clinical infection
  • Give patient 'safety net instructions' and review swab results at 3 days to determine the need for antibiotics
  • First line treatment if there is locally spreading cellulitis or other signs of clinical infection:
    • empirical therapy with oral flucloxacillin, 500 mg–1 g (dependent on body mass index), four times a day, to cover staphylococci and Groups A, C, and G streptococci
    • if penicillin-hypersensitive, clarithromycin, 500 mg, twice daily; if penicillin-hypersensitive and on statins, doxycycline, 200 mg stat and then 100 mg daily
    • if cellulitis is persistent, clindamycin is an alternative, 300–450 mg, four times daily; stop clindamycin if diarrhoea develops
    • all antibiotics to be prescribed for 7 days; if there is slow response, continue for a further 7 days
  • Discuss with local microbiologist for any antibiotic advice needed, or treatment choice for methicillin-resistant Saureus
  • Consider need for referral to secondary care if infection is non-responsive or patient is systemically unwell

full guideline from…
www.gov.uk/government/uploads/system/uploads/attachment_data/file/536231/Venous_Leg_Ulcers_Quick_Reference_Guide.pdf

Public Health England. Venous leg ulcers: infection diagnosis and microbiological investigation. London: Public Health England. 
First included: August 2016.