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Diabetic Foot Infection: Symptoms, Causes and Types

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Diabetic foot infection is due to infection of the soft tissue or bone below the ankle bone. It is estimated that if you have diabetes, there is a 15-25% lifetime risk that you would develop a foot ulcer. In Singapore, about 2 major limb amputations are done every day due to diabetes-related ulcers or gangrene.

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What Is Diabetic Foot Infection?

As with all infections, diabetic foot infection occurs when bacteria enter the body through a wound. It can start off with small scrapes, scuffs or blisters, but if left unnoticed and not treated, it can lead to diabetic foot ulcers. Diabetic foot ulcers are not infections, but they often can lead to infections. When diabetic foot ulcers form, bacteria can enter through the ulcer, creating an infection. 

Why Are Those With Diabetes At Risk of Foot Infections?

Foot problems are a common complication if you have diabetes. Why is this so? The below are 3 reasons why:

1. Poor blood circulation 

High blood sugar levels can damage your blood vessels and decrease blood flow to the feet. Poor blood circulation weakens your skin and increases risk of foot ulcers. Due to the reduced blood flow, wound healing is also impaired. In addition, bacteria and fungi thrive due to the high blood sugar levels in your blood. This increases the risk of wound infection, worsening the ulcer.

2. Nerve damage

High blood sugar levels can also damage your nerves. This is known as “diabetic neuropathy”. Due to the damage in your nerves, you might not be able to feel pain even if a wound is present. This increases your risk of injuring your feet. If left unnoticed, a minor injury can escalate to a serious one. 

3. Foot deformity

Nerve damage can also weaken certain foot muscles and contribute to foot deformities, which increases the risk of foot complications due to diabetes. 

What Are the Symptoms of Diabetic Foot Infection?

The symptoms of diabetic foot infection are similar to those of any infection. 

The 5 common signs of infection to look out for at the site of the wound include:

  1. Redness 
  2. Warmth
  3. Swelling
  4. Pain or tenderness 
  5. Purulent secretions (white, yellow or brown fluid, slightly thick in texture)

Sometimes, you might also notice black tissue surrounding the diabetic foot ulcer. This black tissue is also known as eschar. Eschar forms due to the lack of healthy blood flow to the area. 

If the infection is severe, you might also experience fever, chills or shortness of breath. If you experience any of these systemic symptoms, do visit your doctor immediately. 

How Is A Diabetic Foot Infection Diagnosed?

You should see your doctor as soon as possible if you have diabetes and notice any symptoms as described above. Your doctor would do a complete physical examination on your foot to see if there are any local or systemic signs of infection. Seeing your doctor earlier can reduce the risk of any irreversible health issues like amputation

There are 3 key steps involved in diagnosis of a diabetic foot infection. 

1. Determine the extent and severity of infection

Does the infection affect only the skin or has it also affected the muscles, tendons and bone?

To determine if the diabetic foot infection has affected the bone, your doctor might recommend you to do a MRI (magnetic resonance imaging)

2. Identify underlying factors that predispose to and promote infection

The doctor may check for certain underlying factors or reasons that may give you a heightened chance of developing an infection. He/she may check if there is any sensory loss at the feet, foot deformity, and even your blood sugar control. Your doctor may also evaluate if there is any arterial and/ or venous insufficiency (i.e., poor blood circulation in your blood vessels). 

3. Assess what bacteria or microbes is causing the infection

If deep tissue or bone infection is suspected, your doctor might remove some tissue and send the tissue sample to a lab. The lab will then do a bacterial culture, so as to help your doctor identify and determine what type of bacteria is causing the infection, so that he or she can give you the appropriate treatment for your diabetic foot infection.

What Are The Different Types Of Diabetic Foot Infection?

The Infectious Diseases Society of America (IDSA) classifies diabetic foot infection into 4 categories: 

  1. Uninfected: This means that there are no signs of infection in the foot.
  2. Mild infection: The infection only affects the skin and subcutaneous tissue (i.e., the fat cells and connective tissues) and there are at least 2 out of the 5 signs of infection, as stated above. The redness is also less than or equal to 2cm around the wound.
  3. Moderate infection: The infection affects beyond the skin and subcutaneous tissues, and could have affected the bones. Nonetheless, there is no infection or inflammation that is affecting the whole body.
  4. Severe infection: There is systemic infection or inflammation and you might have at least 2 of the following:
    • A fever of more than 38 degree Celsius
    • Higher heart rate
    • Higher number of breaths you take per minute
    • Elevated white blood cell count

In the next article, find out more on how to treat diabetic foot infection and most importantly, how to prevent it.

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