Foot Infection: Cause, Classification, Symptoms, Diagnosis and Treatment

Foot infection results from the inoculation of harmful micro-organisms in side the tissues of the foot. These micro-organisms feed on the tissue and multiply to many numbers. The body's defense system starts to wage a war against these organisms. The out come of this war is pain, redness, swelling and a rise in the temperature.

The extent of damage that occurs in infection depends on the virulence of the micro-organism and the resistance of the host. If the organism is less virulent and the host has good resistance then the extent of the damage will be least. Where as there will be extensive damage if organism is very virulent and the host resistance is poor.

The organism causing the infection and its virulence can only be known after the infection has occurred, where as conditions causing poor host resistance can be evident before hand.

Conditions and diseases that cause poor host resistance include the following

  • Malnutrition
  • Diabetes Mellitus
  • HIV infection
  • People on immunosupressive drugs

Reduced sensation in the foot can also lead to foot infection, as trauma to the foot goes unnoticed because there is no pain. This is commonly seen in

  • Diabetes Mellitus
  • Leprosy
  • Neurological disorders such as stroke

A poor blood supply to the foot causes a delay in healing of wounds leading to persistence and extension of infection. This is usually seen in

  • Diabetes Mellitus
  • Buergers disease (a vascular disease)
  • Lupus

Foot infection can be classified in to two types

  • infections with out any obvious trauma or atraumatic infections
  • infections with a history of trauma or traumatic infection

Each of these can be further classified in to different types

  • Cellulitis or infection of skin and subcutaneous tissues
  • Fascitis or infection of the fascia, tendons and other tissue underneath the skin and subcutaneous tissues
  • Osteomyleitis and infective arthritis which are infection of bone and joints

Atraumatic infections are usually seen in people who are immunodeficient, have sensory loss or have poor blood circulation in the foot. A few such conditions are

  • Diabetes mellitus
  • Leprosy
  • Buergers disease
  • Organ transplant recipients

Traumatic infections can occur by many different ways of injury, a few of which are

  • Accidents such as
    1. industrial accidents
    2. road traffic accidents that can cause crush injuries or de-gloving injuries
  • lawn mower injuries
  • gun shot injuries
  • puncture injuries

Energy of the injury determines the extent of traumatic foot infections. High energy injuries are usually associated with a large wound that may extend to the bone. Fractures and dislocations may be present and there may also be loss of skin, tendons, muscles and bones.

Puncture injuries are usually caused by stepping on nails, wood and glass. Infection can develop over a few hours and causes a increase in the pain followed by the development of swelling. A part of the object may have remained inside. This can be seen on a x ray, ultrasound or MRI scan.

Usual bacteria that cause infection in the foot include

  • Staphylococcus aureus
  • Group A streptococci
  • Pseudomonas aeruginosa

Usual symptoms of foot infection include the following

  • Pain, that can be moderate to severe or throbbing type if pus is present
  • Swelling
  • Redness of the skin
  • Fever and a local increase in temperature at the site of infection

All the above symptoms may not be seen. In diabetes pain, and fever may be absent where as in Buergers disease there may be no redness and swelling. In patients on immunosuppressive medication and steroids swelling may be the only symptom.

Diagnosis of infection is based on symptoms and a clinical examination. Blood investigations and x rays of the foot are also a part of the work-up to corroborate the diagnosis and rule out other conditions that may mimic a foot infection. Flares of systemic lupus erythematosus, vascular diseases, acute gout and tumors can sometimes mimic symptoms of a foot infection.

At times ultrasound, CT scan and MRI may be required to determine the extent of infection before planning surgery for removal of pus and other dead tissue.

Treatment of foot infection depends on the classification and the extent of the infection.

Here we will see the general principles of foot infection treatment which are

  1. Rest and elevation of the foot on one or two pillows to reduce swelling and pain.
  2. Appropriate antibiotics to kill the bacteria.
  3. Surgery to drain the pus if it is present.
  4. Quick removal of all the dead tissue present as it serves as food for bacteria and antibiotic concentration is poor in dead tissue.
  5. Cleaning of the wound with saline and surrounding normal skin with alcohol.
  6. Regular change of dressing. It is preferable to use a paraffin impregnated dressing gauze.
  7. Once the discharge of fluid from the wound decreases then the interval between the dressing changes can be increased.
  8. Chlorine water, povidone-iodine, hydrogen peroxide and chlorohexidine should not be used as they are toxic to normal tissue.

For wounds with a large amount of discharge foam based vacuum-assisted dressings are very useful as they remove the discharge quickly.

All dead tissue has to be removed as early as possible as healing can only begin once the dead tissue has gone. Dead tissue may be skin, fat, fascia, tendons, muscles and even bone depending on the extent of the infection. At times it is difficult to identify what is alive and what is dead. So multiple visits to the operation room may be required to completely remove the dead tissue.

Once all the dead tissue has gone and the wound starts healing then reconstruction of the foot can begin. The goal of reconstruction is to give as normal a foot as possible.

Below is a case study of a patient with cellulitis of the foot.

foot infection

This is a photo of a young man who came to me with infection in the foot and gangrene of the skin and subcutaneous tissues. In this photo the gangrene is not well demarcated, so I kept him on antibiotics for a few days.

foot infection with gangrene

After a course of antibiotics you can see that the gangrene is well demarcated and the swelling has subsided.

foot infection after debridement

This photo is after removal of all the dead tissue. Fresh bleeding can be seen form the wound.

foot infection after regular dressing

After a few days of regular dressing the wound has filled up with granulation tissue and is now ready for skin grafting.

Foot infection wound with skin graft

This photo shows the foot during surgery after it has been covered with skin graft.

foot infection after skin grafting

This photo was take 7 days after the grafting was done and the dressing was opened. You can see that the graft has been accepted nicely.

foot infection wound after acceptance of skin graft

Here you can see that complete healing has taken place and the foot is now fully functional. The whiteness is due to the antibiotic powder the patient was still applying.

Frequently Asked Questions

How can foot infection be prevented?

People who do not have any disease or disorder like diabetes or lupus that makes the foot prone to infection or people with a normal sensate foot can prevent infection by avoiding any type of injury to the foot, because most infections in these persons occur after trauma. And if they ever injure their foot they should clean it thoroughly with tap water and cover it with a clean dressing or cloth and reach the emergency as soon as possible.

People with diabetes, lupus or other disorders that make the feet prone to infection should care for their feet as they care for their face. They should

  • Clean their feet gently.
  • Apply moisturizer.
  • Keep their nails trim.
  • Thoroughly inspect their feet from all sides every day. Can use a mirror if required.
  • Wear comfortable and soft shoes.
  • Keep their feet away from heat and cold.
  • Walk carefully and look where they are stepping.

I hope the information provided on this page was useful. If you have any query you can ask me at the contact me page.

This page was created on 19th November 2010.

Other causes of foot pain...

Hallux Rigidus

Mallet Toe

Hammer Toe


Flat Foot



Sesamoid Fracture

Tarsal Tunnel Syndrome

Heel Pain

Go back from Foot Infection to Foot Pain


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