- Be able to identify and manage common staphylococcal and streptococcal skin infections.
- Be familiar with the range of appearance of other bacterial infections.
- Impetigo is due to superficial skin infection with Staphylococcus aureus and/or Streptococcus pyogenes.
- Impetigo may complicate wound healing, infestations and dermatitis.
- Furunculosis (boils) is due to invasion of the hair follicle by Staphylococcus aureus.
- Staphylococcal skin infections may rarely be complicated by widespread rashes including toxic shock syndrome and staphylococcal scalded skin syndrome.
- Streptococcal skin infections may rarely be complicated by widespread rashes including scarlet fever and toxic shock-like syndrome.
- If staphylococcal infections recur, treat carrier sites (nostrils) and identify underlying skin diseases such as eczema, scabies and head lice.
- Erysipelas, cellulitis and many cases of necrotising fasciitis are most frequently caused by Streptococcus pyogenes, less often by Staphylococcus aureus, enterobacteriae and anaerobes.
Normal skin flora includes harmless staphylococci, micrococci, diphtheroids and yeasts with aerobes on the surface and anaerobes within hair follicles. These bacteria provide some protection against pathogens by competitive interference and production of antibiotics.
Although Staphylococcus aureus is present in the nostrils of about 30% adults, it becomes invasive resulting in infection if there is an injury or other breach of the skin surface such as dermatitis, scabies or head lice.
Staphylococcal infections are contagious, requiring careful attention to hygiene.
- Frequent hand-washing
- Antiseptics for bathing
- Hot wash clothing, bedding, towels
- Avoid sharing clothing and towels
Localised staphylococcal infections:
- Non-follicular infections: impetigo (surface honey-yellow crusting or blisters) and ecthyma (scabs covering full skin thickness ulceration); some cases of cellulitis
- Follicular infections: bacterial folliculitis (surface pustules) and furunculosis (deeper boils). Lesions greater than 0.5cm are classed as abscesses.
Surface infections tend to be itchy, deeper infections are more painful.
Localised staphylococcal infections may be managed using meticulous wound care, antiseptics and topical antibiotics. Oral antibiotics may be prescribed for more extensive or recurrent infections. However, there is increasing prevalence of methicillin-resistant strains of staphylococci so antibiotics should not be prescribed for trivial reasons.
Toxins and superantigens
Some strains of Staphylococci are more pathogenic due to toxins and superantigens and may result in widespread rashes:
- Staphylococcal scarlatina (non-streptococcal scarlet fever)
- Staphylococcal scalded skin syndrome (generalised burn-like peeling skin in infants)
- Toxic shock syndrome (shock in association with fever, rash, swollen peeling hands and feet).
Scalded skin syndrome
Scalded skin syndrome
Impetigo may be caused by Streptococcus pyogenes, when it is characterised by crusts and ulceration. Staphylococcus aureus is usually a co-pathogen. Streptococcal wound infections are painful with surrounding well-demarcated erythema and oedema.
Streptococcal wound infection
Invasive streptococci result in erysipelas (superficial lymphatic invasion) and cellulitis (involvement of subcutis). Early infection is characterised by fever, rigors and malaise. The affected skin becomes red, swollen and painful. These infections must be treated aggressively as they are potentially fatal. Group A streptococci are uniformly sensitive to penicillin and improvement is usually seen within hours of treatment. Erysipelas and cellulitis may recur in the same site and prolonged courses of penicillin are sometimes required prophylactically.
Necrotising fasciitis is a surgical emergency, most often due to Streptococcus pyogenes and less frequently be due to Staphylococcus aureus, enterobacteriae and other organisms. Necrotic tissue must be debrided thoroughly and immediately as a life-saving procedure.
Toxins and superantigens
Some strains of Streptococci are more pathogenic due to toxins and superantigens and may result in widespread rashes:
- Scarlatina (scarlet fever)
- Streptococcal toxic shock-like syndrome (shock in association with fever, rash, swollen peeling hands and feet).
Cutaneous Group A streptococcal infections (Streptococcus pyogenes) can result in post-streptococcal glomerulonephritis and should be treated with systemic antibiotics such as penicillin. These may not prevent later streptococcal complications due to immunological reactions to superantigens, including the skin diseases hypersensitivity vasculitis and guttate psoriasis.
Vasculitis arising 2 weeks after tonsillitis
Guttate psoriasis, arising 2 weeks after tonsillitis
Less common bacterial infections
Less common bacterial infections resulting in cutaneous signs include:
- Diphtheroids: pitted keratolysis, erythrasma and trichomycosis axillaris
- Spirochaetes: syphilis, yaws and pinta, Lyme disease
- Mycobacteria: tuberculosis, leprosy, atypical mycobacteria
- Diplococci: meningococcus, gonococcus.
- Miscellaneous: erysipeloid, cat scratch disease, anthrax
Trichomycosis axillaris (black concretions)
Trichomycosis axillaris (yellow concretions)
Tuberculosis (lupus vulgaris)
Atypical mycobacteria (M. marinum)