Skin and soft tissue infections are something you will see quite often during residency. Two conditions that can look quite similar at first are erysipelas and cellulitis.
Both can cause redness, swelling and pain, but the depth of infection and the appearance of the affected area are different. Once you know what to look for, the distinction becomes much easier.
In a recent Conceptual Medicine session, Dr. Dilip Kumar explains these differences along with the important points about diagnosis, risk factors and antibiotic treatment.
Erysipelas: Look for a Clear Border
Erysipelas is a superficial infection of the skin, mainly involving the upper part of the dermis. It may also involve the lymphatics.
The organism you should think of first is Group A Streptococcus. Staphylococcus aureus can also be responsible, but Group A Streptococcus is the classic organism discussed for erysipelas.
The easiest clinical clue?
A sharply defined, well-demarcated area of erythema.
The redness has a clear edge, unlike cellulitis, where the margins tend to blend into the surrounding skin.
If erysipelas involves the face, a characteristic butterfly-face appearance may be seen.
Who is at risk?
Diabetes is an important risk factor. Other conditions that can increase the risk include:
- Obesity
- Chronic venous insufficiency
- Varicose veins
- Tinea pedis
- Lymphedema
A fungal infection of the feet, such as tinea pedis, is worth remembering because it can act as a risk factor for recurrent skin infections.
How Is Erysipelas Diagnosed?
In most cases, diagnosis is clinical. There is no specific investigation needed to confirm uncomplicated erysipelas.
For uncomplicated cases, the session discusses oral penicillin or penicillin derivatives, with 5–7 days of treatment being sufficient in most cases. Severe infections may need IV antibiotics.
Cellulitis: Think Deeper and More Diffuse
Now compare that with cellulitis.
Cellulitis involves the deeper dermis and subcutaneous tissue, so it is not as superficial as erysipelas.
And the skin findings are different too.
Instead of a sharp border, cellulitis usually produces diffuse, poorly demarcated erythema.
Patients may also have:
- Significant swelling
- Local edema
- Fever, sometimes high grade
- Pain and discomfort
The session discusses Staphylococcus aureus as the common organism to consider in cellulitis, while Group A Streptococcus can also be involved.
Diabetes Again Matters
If you see cellulitis in a patient with poorly controlled diabetes, don’t ignore even a small injury.
A simple scratch or minor trauma can become the starting point for a significant infection.
Other associations include:
- Trauma
- Abscess
- Venous stasis
- Lymphedema
- Chronic non-healing ulcers
There is another important point in diabetic patients: if a chronic ulcer is not healing, think about underlying osteomyelitis as well. The session highlights the role of an X-ray in such a situation.
Erysipelas vs Cellulitis: The One-Minute Revision
If you’re revising this before an exam or trying to remember it during rounds, keep it simple:
| Erysipelas | Cellulitis | |
| Depth | Upper dermis | Deeper dermis + subcutaneous tissue |
| Border | Well demarcated | Poorly demarcated |
| Spread | More superficial | More diffuse |
| Common organism discussed | Group A Streptococcus | Staphylococcus aureus |
| Fever | Can occur | May be high grade |
So the simplest way to remember it is:
Erysipelas → superficial + sharply demarcated
Cellulitis → deeper + diffuse
When Should MRSA Come Into the Picture?
Not every case of cellulitis needs the same antibiotic approach.
If you’re considering MRSA, the patient’s history becomes important.
Two practical risk factors highlighted in the session are:
- Recent antibiotic exposure
- Recent hospitalization
Previous MRSA infection or colonisation and high MRSA prevalence in the community can also influence the decision.
For oral treatment when MRSA coverage is required, the session discusses:
- Cotrimoxazole
- Doxycycline
- Clindamycin
Linezolid is also discussed as an option in selected patients.
What If the Patient Is Seriously Ill?
The approach changes when cellulitis is accompanied by severe sepsis or septic shock.
In such patients, IV treatment may be needed, and the decision about MRSA coverage becomes particularly important.
For MSSA, the session discusses anti-staphylococcal penicillins and first-generation cephalosporins such as cefazolin.
When MRSA coverage is needed in a severely ill patient, options discussed include vancomycin and daptomycin. IV linezolid may also be considered in selected situations.
What Should You Remember From This Session?
If you remember only a few things, remember these:
1. Well-demarcated erythema → Think erysipelas.
2. Poorly demarcated, diffuse erythema → Think cellulitis.
3. Erysipelas is superficial; cellulitis goes deeper.
4. Diabetes is an important risk factor for both.
5. In a diabetic patient with a chronic non-healing ulcer, keep osteomyelitis in mind.
6. Recent antibiotics or hospitalization should raise suspicion for MRSA.
7. Severe infection needs a different treatment approach from an uncomplicated case.
The Take-Home Point
Erysipelas and cellulitis may appear similar when you first see them, but the clinical examination gives you useful clues.
Look at the border, think about the depth of infection, consider the likely organism, and don’t forget the patient’s risk factors.
For a resident, these are the small clinical details that make the topic easier to remember and, more importantly, easier to apply in practice.
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(SSTIs) Explained | Erysipelas vs Cellulitis | Diagnosis & Treatment | Dr. Dilip Kumar
