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Skin infections

Bacterial case challenge 1

An adolescent presents with a 3-week history of painful lesions on his legs and trunk. He is otherwise well.

Select the terms which best describe the morphology of the lesions. # Abscess #! Crusting || Hard surface deposit. Occurs when plasma exudes through an eroded epidermis. It is rough on the surface and is yellow or brown in colour. Bloody or haemorrhagic crust appears red, purple or black. #! Nodule || An enlargement of a papule in three dimensions (height, width, length). It is a solid lesion. # Plaque What is the most appropriate diagnosis: * Ecthyma *! Furunculosis * Erysipelas * Abscess Explanation: The image shows several inflammatory crusted follicular nodules, characteristic of furunculosis. Explanation: Ecthyma is non-follicular ulcerated impetigo. Erysipelas results in erythematous and oedematous plaques. Abscesses are nodules greater than 1cm in diameter full of pus – these lesions could ultimately result in abscess formation. What is the likely organism? *! _Staphylococcus aureus_ * _Streptococcus pyogenes_ * Diphtheroids * _Proprionibacterium acnes_ Explanation: Furunculosis is nearly always caused by Staphylococcus aureus. What is the best way to confirm the infection is due to Staph. aureus? # Smear for wet ground examination #! Swab for microscopy and culture # Scraping for microscopy and culture # Wood’s light examination Explanation: Swab the lesion and transport in standard bacterial blue-top container for microscopy and culture. The microbiology laboratory should gram stain the swab within a few hours and report culture results within 48 hours. Explanation: Wet ground examinations are useful for spirochaetes; scrapings and Wood's light examination are for fungi.

The patient is treated with oral antibiotics. Which one would you select?

# Phenoxymethyl penicillin # Amoxicillin #! Flucloxacillin # Benzyl penicillin Explanation: In New Zealand, 80-90% Staphylococcus aureus is currently (2003) resistant to penicillin and amoxicillin. Penicillinase-resistant penicillins, such as flucloxacillin or dicloxacillin, or the broad-spectrum beta-lactamase inhibitor amoxicillin/clavulanic acid, should be used. Erythromycin can be used in penicillin-allergic subjects but there is 5-10% resistance to this antibiotic.

The furuncles resolve, some leaving small scars. A few weeks’ later he reports he has developed boils again. He consults you again with an infected chin. He feels unwell and has a mild fever.

The image shows numerous pustules and erosions on the beard area, a condition known as “sycosis barbae”.

The severity of the young man’s infection was considered unusual. Refer to NZ DermNet’s article about Staphylococcal infections.

What are some possible reasons why this patient could have excessive infection? Short answer: You should consider whether the patient has an underlying systemic disease that predisposes him to severe staphylococcal infection (e.g. diabetes, leukaemia, human immunodeficiency viral infection), lifestyle factors such as alcoholism and drug addiction, immunosuppressive medication (e.g. systemic steroids and cytotoxics) or a severe underlying skin disease such as atopic dermatitis. Is the infection due to an unusual organism, or if Staphylococcus aureus, has it become resistant to standard antibiotics? Which of the following investigations should be arranged? #! Bacterial swabs of pustules #! Bacterial swabs from nostrils #! Blood count #! Blood glucose # Blood alcohol Explanation: Bacterial swabs of pustules are necessary to ensure there is no unusual organism and to determine sensitivities to antibiotics. Nasal swabs confirm carrier status. Blood count and blood glucose are first line investigations to detect underlying disease predisposing to infection.

Thorough investigation was unable to detect any significant underlying illness, lifestyle factor or immunosuppressing medication, but culture revealed community-acquired methicillin-resistant Staphylococcus aureus.

Management should now include: #! Oral antibiotics # IV vancomycin #! Skin cleansing with chlorhexidine #! Treatment of nostrils with mupirocin ointment tid for 7 days Explanation: Methicillin-resistant Staphylococcus aureus is most often acquired in hospital, but increasing numbers are being reported in non-hospitalised patients. The predominant community strains continue to remain sensitive to macrolides, tetracyclines and sulphonamides. Explanation: In addition to systemic antibiotics, larger pustules and abscesses should be drained and carrier sites such as the nose and groin should be treated with topical antiseptic or antibiotic twice daily for one week (repeated monthly if infection recurs). Antiseptic soap or cleanser should be used for several weeks. Give advice regarding hygiene (wash daily; do not share clothing, towels or bedding) and nutrition (especially need for red meat for iron, fresh fruit and vegetables for vitamin-c). Family carriers should be treated in the same way.