Clinical Notes : Infection and Sepsis

213. Leg Ulcer and Diabetic Foot infection

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Leg ulcer infection


As with cellulitis, diagnosis of infection within a leg ulcer can be challenging.

Few leg ulcers are clinically infected, but most are colonised by bacteria.


 Antibiotics do not promote healing when a leg ulcer is not infected, therefore correct identification of infection is key to maintaining antimicrobial stewardship.


There are many causes of leg ulcer, and it is important that any underlying conditions, such as venous insufficiency and oedema, are managed optimally to promote healing and prevent infection.


Symptoms and signs of an infected leg ulcer include redness or swelling spreading beyond the ulcer, localised warmth, increased pain, or fever.

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Diabetic foot infection

Diabetic foot infection can lead to serious complications that can be limb-threatening.

It is important that treatment is initiated promptly and managed/monitored in the appropriate setting.


As with leg ulcers, most diabetic foot wounds are likely to be colonised with bacteria.


Diabetic foot infection has at least two of the following:

  • local swelling or induration

  • erythema

  • local tenderness or pain

  • local warmth

  • purulent discharge.


Treatment is based on the severity of foot infection and is classified into mild, moderate, and severe:

  • mild: local infection with 0.5 cm to less than 2 cm erythema around the ulcer. Other causes of inflammatory response (e.g. trauma, gout, acute Charcot neuro-osteoarthropathy, fracture, thrombosis, and venous stasis) should be excluded

  • moderate: local infection with more than 2 cm erythema around the ulcer or involving deeper structures (such as abscess, osteomyelitis, septic arthritis, or fasciitis) and no signs of systemic inflammatory response

  • severe: local infection with signs of a systemic inflammatory response (e.g. temperature of more than 38°C or less than 36°C, increased heart rate, or increased respiratory rate). 


Many moderate and all severe infections should be referred to hospital, and all infections not referred to hospital require urgent (within 1 working day) referral to the local diabetic foot services.

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Taking swabs for microbiological sampling

Swabbing of skin infections should be undertaken judiciously due to the possibility of culturing colonising rather than infective organisms, leading to the initiation of inappropriate treatment.

Impetigo, cellulitis, and leg ulcers often have predictable infective organisms and therefore empirical antibiotic treatment without swabbing is suitable in most cases. 

However, it is important that a deep swab is taken for microbiological testing before, or as close as possible to, the start of antibiotic treatment. This allows empirical antibiotic treatment to be changed if needed when results are available.

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It is important to counsel patients to seek medical attention if they become systemically unwell or infection is rapidly worsening at any time.

Diabetic foot infection can lead to serious limb-threating complications so should be reassessed at 1–2 days if not improving.

Cellulitis and leg ulcer infections should be reassessed if symptoms worsen rapidly, the person becomes systemically very unwell, or there is no improvement after 2–3 days.

Impetigo is generally a self-limiting condition so reassessment can be delayed until the end of the 5-day initial treatment period unless symptoms worsen rapidly or significantly at any time.

When reassessing unresponsive skin infections, it is important to reconsider whether the initial diagnosis is correct; for example, herpes simplex can mimic impetigo, and many conditions can present as cellulitis.


Hospital Referral 


Consider hospital referral or seeking specialist advice for all those with symptoms or signs of a more serious condition such as osteomyelitis

  • septic arthritis

  • necrotising fasciitis

  • limb ischaemia

  • gangrene


and for those

  • who are systemically unwell

  • at high risk of complications

  • have spreading infection not responding to oral antibiotics

  • who cannot take oral antibiotics.


Also consider referral or specialist advice for

  • immunocompromised people with widespread impetigo

  • those with bullous impetigo, particularly babies

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Necrotising Fasciitis


In any patient presenting with skin infection, it is vital to exclude necrotising fasciitis, a rare but destructive and rapidly progressive infection that involves deep tissues, fascia, and muscles.


Necrotising fasciitis has a significant mortality rate and may require extensive surgical debridement.


The presenting signs are often non-specific (redness, swelling, and pyrexia); however, patients may be systemically unwell.

The key symptom is pain disproportionate to the clinical signs.


Immediate surgical referral and admission to hospital is vital if the condition is suspected.


Leg ulcer infection: antimicrobial prescribing.

NICE Guideline 152.

NICE, 2020.


Diabetic foot problems: prevention and management.

NICE Guideline 19.

Published: 26 August 2015 Last updated: 11 October 2019




accesses March 2021


Cellulitis - acute

NICE Clinical Knowledge Summary.

accessed March 2019


Infective skin conditions : when is it appropriate to prescribe an antibiotic ?

Dr. Caroline Ward

Guidelines in Practice

June 2020


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