Skin is covered by billions of ‘normal’ commensal bacteria that prevent pathogenic organisms becoming established. But bacterial skin infections are highly prevalent, and without antibiotics may be fatal. It is important to recognise and treat them early.

Avoidance of infection confers survival advantage: fear of skin disease ‘Is it catching, doctor?’ is therefore ‘sensible’.

Common bacteria causing infection include Staphylococcus aureus, Streptococcus pyogenes, Corynebacterium minutissimum, Mycobacterium tuberculosis, Mycobacterium marinum and Spirochaetes.

Cellulitis and Erysipelas

Redness, swelling, heat, tenderness, pyrexia.
Take swabs for culture from fluid or cracked areas.
Treatment: 500 mg flucloxacillin four times daily.
Risks: recurrence, lymphoedema.

Cellulitis

(Figure 18.1) Streptococcus group A or Staphylococcus aureus infection of subcutaneous tissue, typically of lower leg. Diffuse edge.

Erysipelas

(Figure 18.2) Streptococcus group A infection of the dermis. Typically well-defined with red raised edge, on the face, with initial infection around nose or ears.

Impetigo (Figure 18.3)

Superficial infection of epidermis, redness and crusting usually of face in children. Easily infects other children. Non-bullous impetigo is usually caused by Staphylococcus aureus (aureus means ‘gold’ – the colour of the culture) or by Streptococcus pyogenes. Staphyloccocus aureus causes bullous impetigo with blistering.

Treatment: topical mupirocin, systemic flucloxacillin or erythromycin. If undiagnosed impetigo is treated wrongly with topical steroids, it initially improves but then gets worse.