Tinea Pedis: The Child and the Family

In this issue there is an epidemiologic study of dermatophytosis that sets a practical standard for the clinical research needed in this field. It asks how often dermatophytes are present in children with apparently normal feet compared to children with scaly feet (a sign of clinical tinea pedis). The authors investigated this by comparing two samples of children, carefully matched as to age and sex, 100 with scaly feet and 100 without scaly feet. Not of least interest is that their data shows that in a carefully structured study a sample of 100 subjects per population group provides statistically useful data even when, as in tinea pedis, there exists little a priori information from which to predict variance. For this success we suspect that the dermatophytes of tinea pedis deserve some credit. Their remarkably uniform distribution throughout the world apparently makes a random selection of 100 subjects per tested population useful if these populations are matched and narrowed with respect to other variables. This, of itself, is useful to know for those, like ourselves, who plan studies of their own. Thus one of the first things that strikes us in this study is that the 80%Trichophyton rubrum, 13% Mentagrophytes interdigitale,and 7% Epidermophyton floccosumobtained in these children aged 2 to 12 years conforms to the approximately 80%, 15%, and 5%, respectively, reported in most locations worldwide from the adult population. Frankly we would not have expected this, because we have argued that there are distinct clinical differences and probable epidemiologic differences between these three dermatophytes causing tinea pedis and associated infections of the skin and nails. We have published pedigrees that indicate the T. rubrum is acquired in the family setting with an autosomal dominant pattern of infection, or at least of nail bed onychomycosis. This study of children suggests, however, that tinea pedis in children is a thin slice of the same loaf as tinea pedis in adults, with a prevalence somewhere between the 15% culture-positive results obtained from children with scaly feet and the 4% culturepositive results obtained from children with normal feet. The authors did examine 51 relatives of fungus-positive children and found 24% to 30% of those with lesions fungus-positive, which is less than the 50% or more expected from siblings and parents in completely penetrant autosomal dominant heredity. The prevalence in relatives of fungus-negative children remains to be determined. The isolation of 3%T. rubrumand 1%T. tonsurans from children with normal feet could be explained as skin contamination in an infected environment. However, the questions still remain whether tinea pedis is acquired most commonly during childhood, and whether fungus growth in the stratum corneum can occur or initiate without visible lesions. The data shows that plantar infection can be demonstrated in 57% of fungus-positive children, which we are personally pleased to see, since undo emphasis is usually placed on toe web lesions. However, no data are given on the prevalence or type of onychomycosis in this study, a point of particular interest to us, since the age of onset of onychomycosis in infected children can be very early. The occurrence of scaling in the apparent absence of dermatophytes is the other side of the coin, and probably applies to adults and children alike more often than is appreciated. The purpose of this commentary is to encourage further studies of this quality on the frequency, age of onset, and role of childhood infection in the epidemiology of tinea pedis. In doing so, special note should be taken of the fact that both plantar and interdigital skin was cultured routinely by these investigators.