Diabetic foot infection

Dr Paul Chadwick

Consultant Microbiologist

Salford Royal Hospital

Case History

• A 76 year old man was admitted as an emergency with a red and swollen right foot

• Apyrexial and haemodynamically stable

• Diagnosed with type 2 diabetes two years earlier

• Oral hypoglycaemic therapy: blood sugar control moderate

Investigations

• X-ray of the foot showed changes consistent with both osteomyelitis and soft tissue infection

• C-reactive protein 219 mg/l (<10mg/l)

• Neutrophils 19.2 x109/l (4-11 x109/l)

• Plasma glucose 24.6 mmol/l (3-6 mmo/l).

Illustration reproduced with permission from Clinical Publishing Ltd, Oxford

Diagnosis & Initial management

• Moderate diabetic foot infection– limb-threatening– critical ischaemia not present

• Treated empirically with IV vancomycin and piperacillin/tazobactam

Microbiological investigation

• Polymicrobial infection– Gram stain of pus showed neutrophils, Gram

positive cocci and Gram positive bacilli– Enterocoocci and alpha-haemolytic

Streptoccoci were isolated from pus– At least five different species comprising

Gram positive cocci and Enterobacteria were cultured from superficial swabs.

Surgical Intervention

• On day 4 debridement was undertaken to remove infected bone and soft tissue

• Enterococcus faecalis, Propionobacterium sp. and Escherichia coli were isolated from deep pus and tissue samples.

Further management

• On day 7 antimicrobial therapy was changed to oral amoxicillin plus ciprofloxacin.

• 4 weeks of antimicrobial therapy were given in total

• Ongoing wound and foot care was provided by the Podiatry team

Diabetic foot infection

• Most common reason for diabetes-related admission to hospital

• High morbidity – may result in amputations

Why does DFI occur?

• Foot ulceration is the major factor and occurs secondary to peripheral neuropathy and/or vascular insufficiency (neuro-ischaemic foot ulceration)

• Hyperglycaemia and other metabolic disturbances contribute through immunological (e.g. neutrophil) dysfunction and poor wound healing

Prevention of DFI

• Appropriate foot care/pressure relief– Podiatry services

• Good glycaemic control– Specialist diabetes services

CID 2004; 39:885-910

Multidisciplinary Foot-care Team

• Physician

• Podiatrist

• Medical Microbiologist/ID Physician

• Vascular surgeon

• Foot surgeon

• Radiologist

Microbiological Samples

• Samples should be collected following cleansing and debridement

• Deep soft tissue samples should be obtained from the base of an ulcer by curettage, or at surgery

• Bone biopsy (including histopathological examination) is important in establishing a diagnosis of osteomyelitis

• Samples should be transported without delay to the laboratory and cultured under both aerobic and anaerobic conditions.

Microbiological pathogens

Infection is typically polymicrobial where ulceration is present

• Aerobic Gram positive cocci– Staphylococcus aureus– Β-haemolytic streptococci

• Enterococci• Enterobacteriaceae• Obligate anaerobes• (Nonfermentative Gram negative rods)• (Candida spp.)

Diagnosis and Assessment

• DFI is diagnosed clinically by signs and symptoms of inflammation

• Infections are categorized as mild, moderate or severe, on the basis of clinical and laboratory features

• Assessment is made as to whether an episode is life or limb threatening

Categorization helps to guide appropriate clinical management

Mild infection

Purulent or inflamed wound present• Limited to skin and superficial soft tissues• Inflammation extends <2cm from wound• Not systemically unwell

Treatment usually by oral routee.g. flucloxacillin, doxycycline, clindamycin

Microbiological sampling not routinely required for mild infection unless recent antimicrobial therapy or previous antibiotic-resistant organisms

Moderate infection

Purulent or inflamed wound present in a patient who is systemically well and/or one of the following

• inflammation extends >2cm from wound• lymphangitis• spread beneath superficial fascia• abscess formation• necrosis or gangrene• involvement of muscle, tendon, joint or bone

Treatment by oral or parenteral routes according to clinical assessment and choice of agent

Moderate infection

Treatment options include• amoxicillin/clavulanate• clindamycin + ciprofloxacin• rifampicin + levofloxacin• piperacillin/tazobactam• ertapenem

NB. Choices influenced by local policy with consideration of local issues such as C. difficile and MRSA incidence

Add glycopeptide, linezolid or daptomycin if MRSA infection is suspected or infection is life/limb-threatening

Severe infection

Infection in a patient with evidence of systemic inflammatory response syndrome

IV treatment, at least initially, as an inpatient, e.g.• clindamycin + ciprofloxacin• piperacillin/tazobactam• meropenem or imipenem/cilastatin

Add glycopeptide, linezolid or daptomycin if MRSA infection is suspected or infection is life/limb-threatening

Duration of Antimicrobial Therapy

• Continued until the signs and symptoms of infection have resolved (ulcer may persist)

• Mild soft tissue infections 1-2 weeks• Moderate-severe soft tissue 3-4 weeks

Osteomyelitis typically 6 weeks, unless all affected bone is completely removed by surgery (1-2 weeks)

• Therapy ≥3 months sometimes required for extensive bone infection e.g. calcaneumNB. Courses may need to be longer than for non-diabetic patients with cellulitis

Antibiotics in DFI

• Antimicrobial therapy can be challenging!• Consider patient factors (e.g. age, renal

function, peripheral vascular disease)• Side effects are common

– Gastrointestinal intolerance of oral antibiotics, often to multiple agents

– Hypersensitivity reactions (typically skin rashes)

• Deterioration in renal function may occur

Does the patient require surgery?

Surgical intervention is often required. Urgent assessment is needed by a surgeon with expertise in foot surgery where the infection is life- or limb-threatening. Vascular surgery may be needed where there is critical ischaemia.

? Excision & drainage? Debridement? Resection +/- reconstruction? Revascularisation? Amputation

Wound Care Issues

• Ongoing debridement of non-viable tissue as required

• Dressings to allow daily inspection of wound and to encourage a moist wound-healing environment

• Remove pressure from the wound (off-loading)

Glucose Control

Good blood glucose control should be achieved

• To manage the acute infection

• To reduce the risk of future foot problems

Diagnostic Imaging 1

• Imaging should always be considered to identify soft tissue abscesses or osteomyelitis

• Osteomyelitis is present in 30% DFI• It is important to identify underlying osteomyelitis

as this influences the choice, dose, route and duration of antimicrobial therapy, however

• There is no single, non-invasive, highly sensitive and specific test for osteomyelitis

Diagnostic Imaging 2

• If osteomyelitis is suspected and initial X-ray does not confirm the presence of osteomyelitis, use magnetic resonance imaging (MRI).

• If MRI is contraindicated, white blood cell (WBC) scanning may be performed instead

NICE clinical guideline 119

Clinical signs of osteomyelitis

The following are associated with osteomyelitis

• Inflamed, swollen (‘sausage’) toe

• Presence of exposed bone

• Positive ‘probe-to-bone’ test

‘Sausage toe’

Osteomyelitis of halluxProbe to bone?

X-rays and DFI

• Plain X-rays can be negative during the first 2-3 weeks of osteomyelitis

• Charcot neuroarthropathy & gout may produce similar appearances

• Pragmatic approach where osteomyelitis is suspected but X-rays are negative– treat for osteomyelitis for two weeks then re-Xray– extend the course of therapy if new changes become

apparent.

Osteomyelitis distal phalanx

MR imaging and DFI

• Marrow oedema• Cortical discontinuity• periosteal reaction• debris• sequestra• soft tissue oedema/induration• joint involvement• ulceration• sinus formation• abscess collection

Osteomyelitis of calcaneum, T1 image

Image courtesy of Dr J Harris, Radiology Department, Salford Royal Hospital

Sinus

Marrow oedema

Marrow oedema

Soft tissue oedema

Osteomyelitis of 1st metatarsal head, STIR image

Image courtesy of Dr J Harris, Radiology Department, Salford Royal Hospital

OPAT and DFI

Outpatient (or home) parenteral antimicrobial therapy may be appropriate as prolonged IV therapy often needed for

• Severe infection

• Osteomyelitis

• MRSA infection

• Intolerance of oral agents

• No response to oral agents

Patient eligibility for OPAT

• Medically stable

• Appropriate IV access

• Home circumstances appropriate– Support– Communications– Facilities

PICC lines