Diabetic Foot Infection

Why foot infections are dangerous in diabetes

Three problems combine:

• Neuropathy: diabetic peripheral neuropathy removes protective feeling, so a stone in a shoe or a blister goes unnoticed for days. It also dries the skin, which cracks.
• Poor circulation: peripheral artery disease reduces the oxygen, immune cells and antibiotics that reach the wound.
• Weaker immune response: high blood sugar impairs white blood cells.

About half of diabetic foot ulcers become infected, and around 1 in 5 moderate or severe infections ends in some level of amputation. The foot's compartments and tendon sheaths let infection track deep and spread quickly.

Signs of infection in a diabetic foot

Classic signs may be muted because of nerve damage and poor blood flow. Look for:

• redness spreading from the edge of the wound
• warmth, swelling or firmness around it
• pus or cloudy, increasing drainage
• a foul smell
• new pain or tenderness in a foot that is usually numb
• the ulcer getting bigger, deeper or changing color (gray, yellow or black tissue)
• a probe or swab reaching bone
• unexplained high blood sugars, fatigue or fever

Many people with severe infection have no fever. Absence of fever does not rule it out.

How doctors grade severity

The IWGDF/IDSA system guides treatment:

Infection involving bone is noted separately as osteomyelitis.

Diagnosis

1. Examination: depth of the ulcer, a sterile metal probe to see if it reaches bone, pulses, sensation and footwear.
2. Tissue sample for culture: taken from the base of the cleaned wound or by biopsy. Surface swabs are less reliable.
3. Blood tests: white cell count, CRP and ESR (a very high ESR suggests bone infection), blood sugar and kidney function.
4. X-ray: looks for bone damage, gas in tissue and foreign bodies.
5. MRI: the best test for osteomyelitis and deep abscess.
6. Circulation tests: ankle-brachial index, toe pressures or Doppler ultrasound.
7. Bone biopsy: confirms osteomyelitis and identifies the bacteria when the diagnosis is uncertain.

The most common bacteria are Staphylococcus aureus (including MRSA) and streptococci. Chronic, deep or previously treated wounds often have several bacteria, including gram-negative and anaerobic types.

Treatment

Antibiotics

• Mild infections: oral antibiotics targeting staph and strep, usually for 1 to 2 weeks.
• Moderate or severe: broader antibiotics, often IV at first, adjusted to culture results.
• Osteomyelitis: usually about 6 weeks, or shorter if all infected bone is removed surgically.

Antibiotics are not used for ulcers that are not infected.

Surgery and wound care

• Debridement: removing dead and infected tissue is often needed to let the wound heal.
• Drainage of abscesses, and urgent surgery for gas-forming or necrotizing infection.
• Removal of infected bone or, when the foot cannot be saved, a toe, ray or partial foot amputation. The aim is to keep as much of the foot functional as possible.

Off-loading

Walking on an ulcer keeps it open. A total contact cast, removable walker boot or special shoes take pressure off the area.

Restoring blood flow

If circulation is poor, a vascular surgeon may perform angioplasty or bypass. Without enough blood flow, infections often do not heal.

Blood sugar control

High glucose slows healing and feeds infection. Insulin is often adjusted during treatment.

A multidisciplinary foot team (podiatrist, diabetes specialist, vascular surgeon, infectious disease specialist, wound nurse) improves limb salvage.

Complications

• Spread to bone, joints and tendons
• Gangrene from infection plus poor blood flow
• Sepsis
• Amputation, with a high risk of a further ulcer on the other foot
• Recurrence: about 40% of people have a new ulcer within a year of healing

Prevention

See diabetic foot care for full prevention advice. The essentials:

• Check both feet daily, including the soles and between toes, with a mirror or a helper.
• Never walk barefoot, even at home. Check shoes for stones before putting them on.
• Wash and dry feet carefully and moisturize the skin, but not between the toes.
• Have toenails, corns and calluses treated by a podiatrist if you have neuropathy or poor circulation.
• Get a foot exam by a clinician at least once a year, more often if you are high risk.
• Keep blood sugar, blood pressure and cholesterol in range, and stop smoking.

Frequently asked questions

What does an infected diabetic foot ulcer look like?

The skin around it is red, warm and swollen, often with pus, a bad smell and gray, yellow or black tissue in the base. The ulcer may get larger or deeper. Pain may be absent if you have nerve damage, so look for visual changes rather than relying on how it feels.

Can a diabetic foot infection heal on its own?

No. Infected diabetic foot wounds need antibiotics and usually professional wound care, debridement and off-loading. Waiting allows infection to spread to deeper tissue and bone. See a doctor the same day if a foot wound shows signs of infection.

How do I know if the infection has reached the bone?

Signs include an ulcer that has lasted weeks over a bony area, bone you can see or touch with a probe, a swollen red "sausage" toe, and a very high ESR blood test. MRI or bone biopsy confirms osteomyelitis.

How long does it take to treat a diabetic foot infection?

Mild skin infections usually need 1 to 2 weeks of antibiotics. Deeper soft tissue infections may need 2 to 4 weeks, and bone infection about 6 weeks unless the infected bone is removed. The wound itself often takes much longer to heal fully.

Why do people with diabetes need amputations?

Amputation is needed when infection or gangrene destroys tissue that cannot be saved, often because poor circulation stops healing. Most amputations start with a foot ulcer, which is why daily foot checks and fast treatment of small wounds prevent so many of them.