Dermatology, Venereology and Leprosy
Pyoderma and Bacterial Skin Infections
Pyoderma for MBBS and NEET-PG: impetigo, folliculitis, furuncle and carbuncle, erysipelas versus cellulitis, Gram stain and antibiotic treatment, mapped to NMC codes DR15.
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Pyoderma and Bacterial Skin Infections
Pyoderma for MBBS and NEET-PG: impetigo, folliculitis, furuncle and carbuncle, erysipelas versus cellulitis, Gram stain and antibiotic treatment, mapped to NMC codes DR15.
Pyodermas are the pus-forming bacterial skin infections that recur in examinations. This chapter covers impetigo and its complications, the follicular infections from folliculitis to carbuncle, erysipelas and cellulitis, the Gram stain, staphylococcal toxin syndromes, and the choice between topical and systemic antibiotics and surgical drainage.
High-yield: Pyoderma and Bacterial Skin Infections
- Pyodermas are pus-forming bacterial skin infections, most commonly caused by Staphylococcus aureus and Streptococcus pyogenes.
- Impetigo is a superficial infection with golden or honey-coloured crusts, common in children and highly contagious.
- Non-bullous impetigo is usually streptococcal or staphylococcal, while bullous impetigo is caused by toxin-producing Staphylococcus aureus.
- Post-streptococcal glomerulonephritis is a recognised complication of streptococcal impetigo.
- Folliculitis is inflammation of the hair follicle, presenting as small follicular pustules.
- A furuncle or boil is a deeper infection of the follicle, and a carbuncle is a coalescence of several furuncles with multiple draining points, often in diabetics.
- Erysipelas is a well-demarcated, raised, painful red infection of the upper dermis, usually streptococcal and often on the face or leg.
- Cellulitis is a deeper, less well-defined infection of the dermis and subcutaneous tissue, warm, tender and spreading.
- A Gram stain of pus shows Gram-positive cocci in clusters for staphylococci and in chains for streptococci.
- Staphylococcal scalded skin syndrome, caused by exfoliative toxin, produces widespread superficial peeling in young children.
- Localised superficial pyoderma such as impetigo can be treated with topical antibiotics like mupirocin.
- More extensive infection, furuncles, carbuncles, erysipelas and cellulitis need systemic antibiotics such as flucloxacillin, with cover adjusted for local resistance patterns.
- Surgical incision and drainage is required for a fluctuant abscess or carbuncle, as antibiotics alone do not clear a collection of pus.
- Recurrent boils, carbuncles and severe infection should prompt a search for diabetes, poor hygiene and nasal staphylococcal carriage.
Common pyodermas
- **Impetigo:** Honey-coloured crusts, children; watch for post-streptococcal nephritis.
- **Folliculitis to carbuncle:** Follicular pustule, boil, then coalescent carbuncle; diabetes link.
- **Erysipelas versus cellulitis:** Erysipelas well-demarcated raised upper dermis; cellulitis deeper and diffuse.
- **Treatment:** Topical for localised impetigo; systemic antibiotics and drainage for abscess.
NMC competencies in this chapter
- **DR15.1:** Distinguishing folliculitis, impetigo and carbuncle from other lesions
- **DR15.2:** Identifying staphylococci on a Gram stain
- **DR15.3:** Indications and pharmacology of drugs used in pyoderma
- **DR15.4:** Indications for surgical referral in bacterial skin infection
Frequently Asked Questions
What does impetigo look like?
A superficial infection with golden or honey-coloured crusts, common in children and highly contagious. Streptococcal impetigo can be followed by post-streptococcal glomerulonephritis.
What is the difference between a furuncle and a carbuncle?
A furuncle or boil is a deep infection of a single hair follicle, while a carbuncle is a coalescence of several furuncles with multiple draining sinuses, often seen in people with diabetes.
How do erysipelas and cellulitis differ?
Erysipelas is a well-demarcated, raised, usually streptococcal infection of the upper dermis, while cellulitis is a deeper, less sharply defined infection of the dermis and subcutaneous tissue.
When is surgery needed in pyoderma?
A fluctuant abscess or carbuncle needs incision and drainage, because antibiotics alone cannot clear a walled-off collection of pus.
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