Common skin infections in children: Impetigo and tinea capitis

In the second of this series about children's skin infections, Michael J Sladden and Graham A Johnston give an evidence based approach to the diagnosis and treatment of impetigo and ringworm

Most children will have a skin infection at some time. Skin infections are a common reason for consultation, both in primary care and in dermatology practice.^{w1 2 3} We review two more common skin infections in children (impetigo and ringworm) and describe their epidemiology, clinical features, and treatment, focusing on treatments with best evidence.

Impetigo

Cutaneous staphylococcal and streptococcal infections are important in children. They cause a wide spectrum of illness depending on the site of infection, the organism, and the host's immunity.^w4 Impetigo is a superficial skin infection characterised by golden crusts (fig 1). It is caused by Staphylococcus aureus or Streptococcus pyogenes.

Impetigo is the third most common skin disease in children, after dermatitis and viral warts, with a peak incidence at 2-6 years of age.^w56

Lesions are highly contagious and can spread rapidly by direct contact, through a family, nursery, or class.^w7

The condition is more common in children with atopic dermatitis, in those living in tropical climates, and in conditions of overcrowding and poor hygiene. Nasal carriage of organisms may predispose to recurrent infection in an individual.

Impetigo can occur either as a primary infection or secondary to another condition, such as atopic dermatitis or scabies, which disrupts the skin barrier. It can be classified clinically as impetigo contagiosa (non-bullous impetigo) or bullous impetigo. Impetigo contagiosa is caused by S aureus or S pyogenes. Bullous impetigo is invariably caused by toxin, producing S aureus.

Impetigo, showing classic golden coloured crust

Impetigo contagiosa

Impetigo contagiosa is the most common form of impetigo. Lesions begin as vesicles or pustules that rapidly evolve into gold crusted plaques, often 2 cm in diameter. They usually affect the face and extremities and heal without scarring. Constitutional symptoms are absent. Satellite lesions may occur due to autoinoculation.

Bullous impetigo

Bullous impetigo is characterised by flaccid, fluid filled vesicles and blisters (bullae). These are painful, spread rapidly, and produce systemic symptoms. Lesions are often multiple, particularly around the oronasal orifices, and grouped in body folds. To confirm the diagnosis and to target treatment Gram's stain, culture, and sensitivity testing should be carried out on the exudate from lesions.

Treatment

Treatments for impetigo include topical and systemic antibiotics and topical antiseptics.^w8 Topical mupirocin and fusidic acid have been shown to be safe and effective treatments for mild impetigo.^w8 In mild cases they are probably as effective as oral antibiotics.^w8 To minimise the development of resistant organisms, use the topical antibiotics that are available in cream form only, which are not available as systemic preparations.

Oral antibiotics

Oral antibiotics may be better than topical preparations for more serious or extensive disease; they are easier to use but have more side effects than topical agents. Flucloxacillin is considered the treatment of choice for impetigo.^w9 Macrolides, cephalosporins, and coamoxiclav are also reported to be effective, but evidence is limited because the studies have not been performed.^w8 Selection of systemic antibiotic is determined by factors such as local epidemiology of resistance, patients' allergy or intolerance, and proved bacterial sensitivity after microbiological assessment.

If oral antibiotics are needed, we recommend as first line treatment a seven day course of flucloxacillin. In cases of allergy to penicillin, erythromycin (or similar macrolide) is suitable, but in some patients this causes gastrointestinal disturbance, and resistance to erythromycin is increasing. For impetigo caused by erythromycin resistant organisms, cephalosporins such as cephalexin are effective, although 10% of patients who are sensitive to penicillin are also sensitive to cephalosporins. Coamoxiclav (amoxicillin and clavulanic acid) is effective in infections caused by b lactamase producing strains of S aureus. Bacteriological culture is important before changing to this drug.

Topical antiseptics

Although no clear evidence supports the role of topical antiseptics in impetigo, they do help to soften crusts and clear exudate in mild disease. In more severe cases they may be a useful adjunct to antibiotics.

We suggest using topical mupirocin or fusidic acid for seven days in clinically mild impetigo. Oral antibiotics should be reserved for recalcitrant, extensive, systemic disease.

Tinea capitis (scalp ringworm)

Tinea capitis (scalp ringworm) is a highly contagious infection of the scalp and hair caused by dermatophyte fungi. It occurs in all age groups, but predominately children. It is endemic in some of the poorest countries.^w10

The commonest cause of tinea capitis worldwide is Microsporum canis.^w11

The epidemiology of tinea capitis in the United Kingdom has recently changed dramatically,^w12 reflecting a similar trend in the United States 20 years ago.^w13 In the United Kingdom it is becoming a major public health problem, and Afro-Caribbean children are particularly affected.^w14 The predominant organism was M canis, but now Trichophyton tonsurans causes 90% of cases in the United Kingdom and the United States.^w12 T tonsurans is an anthropophilic fungus, which spreads from person to person. The reason for this change is unclear, but hairdressing practices such as shaving the scalp, plaiting, and using hair oils may increase spread.^w12

Tinea capitis causes patchy alopecia, but specific clinical patterns can be varied. There are 6 main patterns (box).^w15

The differential diagnosis for tinea capitis includes seborrhoeic dermatitis, atopic dermatitis, psoriasis, alopecia areata, and alopecia folliculitis. Tinea capitis should be considered in every child with a scaly scalp because the infection is common and the presentation diverse. Only 7% of children receive appropriate treatment for tinea capitis before referral to dermatology practice.^w15

Grey type tinea capitis with inflammation, erythema, scaling, pastules, and crusting

Treatment

If tinea capitis is suspected, specimens of hair and scale should be examined to confirm the diagnosis. The aim of treatment is to provide a quick clinical and mycological cure, with minimal adverse effects and spread of disease. This requires oral antifungal agents, although topical treatment may reduce the risk of transmission at the start of systemic therapy.

Griseofulvin is the only treatment for tinea capitis licensed in the United Kingdom. It has been the treatment of choice for 40 years, with good evidence of efficacy in infections caused by T tonsurans and M canis.^{w16 - 18} The recommended dose in children is 10 mg/kg/day, although some authors advocate up to 25 mg/kg/day. Treatment is taken until clinical and mycological cure is documented, usually about eight weeks. Side effects include nausea and rashes (about 10%); griseofulvin is contraindicated in pregnancy.

Good evidence supports the use of terbinafine for treating tinea capitis caused by T tonsurans^{w16 - 18} it may be less effective for M canis. The dose ranges between 3 and 6 mg/kg/day for four weeks. Side effects include gastrointestinal upset and rashes (about 5%). Itraconazole, fluconazole, and ketoconazole are reported to be effective in tinea capitis, but there is less supportive evidence.

Michael J Sladden specialist registrar, affiliation
Email: m.sladden@doctors.org.uk

Graham A Johnston, consultant, Department of Dermatology, Leicester Royal Infirmary, Leicester


studentBMJ 2005;13:177-220 May ISSN 0966-6494

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