Common Skin Infections

Impetigo

Unlike most skin disease, impetigo is a highly infectious skin disease (spread by direct contact - family/school). It is a very common condition and is most common in children. It typically presents with weeping, exudative areas with a typical honey coloured crust on the surface (esp face and hands). If you see it in an adult, you should consider whether the patient plays contact sports ('scrum pox' when spread by rugby players), has an underlying immune disorder, or whether you are seeing 'impetiginisation' of another dermatological problem i.e. secondary staphylococcal infection superimposed on a primary dermatological condition such as nummular dermatitis. It can cause blistering ("bullous impetigo") due to bacterial toxins. Over 90% of cases are caused by Staphylococcus aureus, but rarely group A Streptococci can be responsible, so taking swabs is important.

 

Bullous impetigo in a child. Note annular appearance                                         Impetigo in an adult (HIV associated)

 

 

We probably overuse oral antibiotics for this condition. Localised disease can be treated with topical fucidin (three times daily) and the antiseptic povidone iodine for 1 week. In very weepy impetiginised eczema I sometimes suggest using Potassium permanganate soaks (dilute KMNO4 to pale pink solution and apply on gauze for 20 mins. Remember it stains nails and washbasins etc brown - make it up as a dilution on an old plastic bowl not the posh sink!). For more extensive disease, oral antibiotics for 7-10 days (flucloxacillin 500mg four times daily for staphylococcus; Penicillin V 500mg four times daily for streptococcus) should be used. In hospital practice we often use a combination such as CoAmoxiclav but in the community setting this practice has recently been discouraged due to the threat of increased bacterial resistance. Other close contacts should be examined and children should avoid school whilst lesions are weepy and crusty. Recurrent impetigo may occur, often due to resistant bacteria e.g. MRSA. In these cases take skin swabs for bacteria (MRSA) and check other family members. I often take nasal swabs and consider Nasal staphylococcal eradication – e.g. mupirocin (three times daily for 1 week) to eradicate nasal carriage +/-treat whole family with antibiotics/chlorhexidine. If this doesn't work, then you should consider whether there is underlying immunosuppression/diabetes.

Cellulitis

Cellulitis is a hot, sometimes tender area of confluent erythema of the skin and is usually caused by a streptococcus (occasionally staph/gram negatives). There may be a portal of entry for infection such as a recent abrasion or a venous leg ulcer. Web spaces of the toes should be examined for evidence of fungal infection. It often affects the lower leg causing an upwards spreading, hot erythema. Patients are nearly always unwell and pyrexial. It may also be seen affecting one side of the face - hot, well-demarcated swollen erythema- when it is known as Erysipelas.

Clinical Tip; Erysipelas often starts just under the eye or at the bridge of the nose and has a surprising amount of oedema. It may resemble an allergic contact dermatitis initially but the clue is that in erysipelas the patient is unwell.

Occasionally, as well as the signs described above, one can see blistering of the skin.

Diagnosis is nearly always made on clinical grounds as blood cultures are often negative. Confirmation of infection, if necessary, is best done serologically by streptococcal titres (ASOT).

In the early stages oral Penicillin or Erythromycin 500 mg twice daily (bd) may suffice. However it is important to have a low threshold for admission to hospital for IV antibiotics as cellulitis may be fatal. It may be recurrent, particularly in those patients with underlying lymphoedema or venous hypertension, and long term low dose antibiotic prophylaxis should be considered in high risk individuals.

Clinical Tip: Note that cellulitis is unilateral! It is VERY rare to see it bilaterally. Junior casualty officers often refer 'bilateral cellulitis' when in fact the diagnosis is usually varicose eczema with venous hypertension, allergic contact dermatitis to bandages or lipodermatosclerosis.

 

Cellulitis – hot, red leg. Note blistering also.

Post-operative cellulitis – note the marking to indicate if improvement occurring

Erysipelas of ear

Erysipelas- note the typical initial location under eye and at bridge of nose with significant oedema

Dissecting Cellulitis of the Scalp is really rather a misnomer as it is not a cellulitis! it is a condition seen young to middle-aged men with skin type 6 and consists of painless, deep, firm nodules, over the scalp. There may be marked bogginess and sinus tracts. Treatment is difficult but oral tetracyclines or intralesional corticosteroids. It is discussed in more detail in the module on Hair Disorders. I include it here for completeness.