Am Fam Physician. 2000;61(5):1463-1464
Once they enter school, the most common fungal infection in children is tinea capitis, which is usually caused by Trichophyton tonsurans. Clinical findings may include dandruff-like flaking, with minimal or no hair loss.
Because clinical findings may be subtle and nondiagnostic, confirmation of the diagnosis by microscopic examination or fungal culture is necessary. The traditional method of obtaining a culture consisted of scraping scale and hair with a no. 15 scalpel blade or plucking hairs from the scalp. Either of these methods may be difficult to use with a small, uncooperative child. Other methods have included using toothbrushes, hairbrushes, wet gauze and adhesive tape to collect specimens. A potassium hydroxide test is useful in the diagnosis of cutaneous fungal infections, but assessment of hair and scalp samples is often difficult to interpret, and interobserver variability is high. Friedlander and associates compared the accuracy of the cotton swab technique with that of the toothbrush method in identifying fungal infections of the scalp, and assessed effects of specimen transport and conditions on the sensitivity and specificity of the technique.
Children who presented with symptoms suggestive of tinea capitis (e.g., pruritus, hair loss, erythema and posterior cervical adenopathy) were included if they had no kerion and no history of recent use of antifungal treatment. During part one of the study, two cultures were obtained from each participant; the sequence of the methods was randomly assigned. A sterile toothbrush was rubbed gently over two affected areas of the scalp. The surface of the toothbrush was then inoculated onto Mycosel medium. The second culture was obtained with a sterile cotton-tip applicator (moistened with tap water) that was rubbed over an affected area of scalp. The swab was then inoculated onto Mycosel medium. Samples were evaluated in-office for three weeks.
Part two of the study consisted of obtaining samples with two cotton swabs. One sample was obtained and managed as above (cotton-swab sample, inoculation onto Mycosel medium and in-office analysis). The other sample was sent to an outside laboratory in a standard bacterial culturette transport medium. This sample was obtained with the culturette swab provided in the transport medium, and the swab was moistened with the transport medium from the bottom of the tube.
During part one of the study, 100 samples were collected from 50 children between the ages of 10 months and 12 years. After exclusion criteria, 44 samples were positive for T. tonsurans, eight samples were positive for Microsporum canis, four samples were positive for Candida albicans, two samples were positive for Trichophyton violaceum and in 38 samples no growth was noted after four weeks. Complete concordance was noted between the toothbrush and the cotton-swab methods.
During part two of the study, the investigators collected 62 samples from 31 patients between the ages of two months and 25 years. After exclusion criteria, 56 samples were analyzed: 28 samples grew a dermatophyte species, 24 samples grew T. tonsurans and four samples grew M. canis. Complete concordance between the in-office and outside laboratory findings was noted.
The authors conclude that use of a moistened cotton swab is an easy, reproducible method of obtaining a fungal culture sample from the scalp of small children who may be frightened by other methods. In addition, cotton swabs are more readily available in medical offices than toothbrushes. Delay in plating the specimen (if the specimen is sent to an outside laboratory) does not decrease sensitivity or specificity.