Cellulitis

Introduction | Aetiology and Risk Factors | Clinical Presentation | Diagnosis | Management and Treatment | Complications | When to Refer | References

Introduction

Cellulitis is a common bacterial skin infection that affects the deeper layers of the skin, specifically the dermis and subcutaneous tissues. It typically presents with an area of redness, swelling, warmth, and pain, and it most commonly occurs on the lower legs. Cellulitis can be serious if left untreated, as it may spread to deeper tissues and the bloodstream, leading to systemic infection.

Aetiology and Risk Factors

Cellulitis is primarily caused by bacteria entering the skin through a break or crack in the skin barrier:

• Common Pathogens: The most common causative organisms are Streptococcus pyogenes (Group A Streptococcus) and Staphylococcus aureus. Methicillin-resistant Staphylococcus aureus (MRSA) is also a potential pathogen, particularly in healthcare settings.
• Risk Factors:
  • Skin Trauma: Cuts, abrasions, surgical wounds, insect bites, or other skin injuries can provide an entry point for bacteria.
  • Chronic Skin Conditions: Conditions such as eczema, athlete's foot, or ulcers increase the risk of cellulitis by disrupting the skin barrier.
  • Peripheral Vascular Disease: Poor circulation in the lower extremities can predispose individuals to cellulitis.
  • Diabetes: Diabetic patients are at higher risk due to neuropathy, poor wound healing, and a compromised immune response.
  • Immunosuppression: Individuals with weakened immune systems, such as those on immunosuppressive drugs or with HIV, are at greater risk.

Clinical Presentation

Cellulitis typically presents with the following features:

• Redness (Erythema): The affected area appears red, and the redness may spread as the infection progresses.
• Swelling: The skin and underlying tissues in the affected area may become swollen.
• Warmth: The affected skin feels warm to the touch, indicating inflammation.
• Pain: The area is often tender or painful, and the pain may worsen with movement or pressure.
• Fever and Malaise: Systemic symptoms such as fever, chills, and general malaise may be present, particularly in more severe cases.
• Lymphangitis: Red streaks may appear, indicating the spread of infection along the lymphatic vessels.
• Blistering or Abscess Formation: In more severe cases, blisters, bullae, or abscesses may develop.

Diagnosis

The diagnosis of cellulitis is primarily clinical, based on the characteristic appearance of the affected area and the patient’s symptoms:

• Clinical Examination: The diagnosis is typically made based on the presence of redness, warmth, swelling, and pain in the affected area. A thorough history should be taken to identify potential risk factors, such as recent trauma or underlying conditions.
• Blood Tests:
  • Full Blood Count (FBC): An elevated white blood cell count may indicate an infection.
  • C-Reactive Protein (CRP): Elevated CRP levels indicate inflammation and can help monitor the response to treatment.
• Blood Cultures: Blood cultures may be taken if the patient is febrile or if there are signs of systemic infection, though they are often negative in cases of uncomplicated cellulitis.
• Swab or Aspiration: If there is an open wound, blister, or abscess, a swab or aspiration may be taken for culture and sensitivity testing to guide antibiotic therapy.
• Imaging: In cases where osteomyelitis (bone infection) is suspected, or if there is no improvement with initial treatment, imaging studies such as X-ray, MRI, or ultrasound may be considered.

Management and Treatment

The management of cellulitis involves antibiotic therapy, supportive care, and addressing any underlying conditions or risk factors:

1. Antibiotic Therapy

• Oral Antibiotics:
  • Flucloxacillin: First-line treatment for uncomplicated cellulitis caused by Staphylococcus aureus or Streptococcus spp.
  • Penicillin Allergy: For patients allergic to penicillin, clarithromycin or erythromycin may be used as alternatives.
  • MRSA: In cases of suspected or confirmed MRSA, doxycycline or trimethoprim-sulfamethoxazole (co-trimoxazole) may be used.
• Intravenous Antibiotics: Severe cases, particularly those with systemic symptoms or risk of complications, may require hospitalisation for intravenous antibiotics such as flucloxacillin, ceftriaxone, or vancomycin.

2. Supportive Care

• Pain Management: Analgesics such as paracetamol or ibuprofen can help relieve pain and reduce fever.
• Elevation: Elevating the affected limb can help reduce swelling and pain, particularly in cases of lower limb cellulitis.
• Hydration: Patients should be encouraged to stay well-hydrated, especially if they have a fever.

3. Addressing Underlying Conditions

• Skin Care: Addressing underlying skin conditions, such as eczema or athlete's foot, can help prevent recurrence.
• Foot Care in Diabetes: Diabetic patients should receive regular foot care to prevent injuries that could lead to cellulitis.
• Compression Therapy: For patients with chronic venous insufficiency or lymphedema, compression stockings or wraps may be recommended to reduce swelling and prevent recurrence.

Complications

If left untreated or inadequately managed, cellulitis can lead to several complications:

• Abscess Formation: An abscess may develop if the infection causes a collection of pus to form within the tissues.
• Lymphangitis: Infection may spread along the lymphatic vessels, causing red streaks and potentially leading to lymphadenitis.
• Sepsis: Bacteria can spread into the bloodstream, leading to sepsis, a potentially life-threatening condition requiring urgent medical attention.
• Osteomyelitis: If the infection spreads to underlying bone, it can cause osteomyelitis, a serious and difficult-to-treat condition.
• Chronic Lymphedema: Recurrent cellulitis can damage the lymphatic system, leading to chronic swelling of the affected limb (lymphedema).

When to Refer

Referral to a specialist or hospital admission may be necessary in the following situations:

• Severe or Rapidly Progressing Infection: If cellulitis is severe, rapidly spreading, or associated with systemic symptoms, hospital admission for intravenous antibiotics may be necessary.
• Immunocompromised Patients: Patients with a compromised immune system, such as those with HIV, cancer, or on immunosuppressive therapy, may require specialist management.
• Recurrent Cellulitis: Referral may be needed for patients with recurrent episodes to investigate and manage underlying predisposing factors.
• Suspected Osteomyelitis: If there is a concern that the infection has spread to underlying bone, referral for imaging and specialist care is necessary.
• Failure to Respond to Treatment: If there is no improvement after 48-72 hours of appropriate antibiotic therapy, referral is warranted to reassess the diagnosis and treatment plan.

References

1. British Association of Dermatologists (2024) Guidelines for the Management of Cellulitis. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Cellulitis: Diagnosis and Management. Available at: https://www.nice.org.uk/guidance/ng103 (Accessed: 26 August 2024).
3. British National Formulary (2024) Antibiotics for Skin and Soft Tissue Infections. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).