Interdigital and Plantar Foot Infections: A Retrospective Analysis of Molecularly Diagnosed Specimens in the United States and a Literature Review

Up to one-quarter of the United States population is affected by tinea pedis (athlete’s foot). Tinea pedis of the web space (interdigital tinea pedis) is a common clinical presentation causing skin macerations and fissures. A “dermatophytosis complex” (i.e., concomitant bacterial colonization) further complicates treatment. Here, we examined records of 14,429 skin specimens taken from the feet of dermatology and podiatry outpatients over a 4.6-year period; all specimens were subjected to multiplex qPCR diagnosis for the detection of dermatophytes, Candida, Corynebacterium minutissimum, Pseudomonas and Staphylococcus aureus. A literature search was conducted to review the reported prevalence of fungal and bacterial agents. In both interdigital and plantar foot specimens, dermatophytes (33.3–33.8%) and S. aureus (24.3–25%) were found to be the predominate pathogens. In the interdigital space, a higher prevalence of C. minutissimum (15.7% vs. 7.9%) and Pseudomonas (23.5% vs. 9.6%) was found. The detection of Pseudomonas was more likely to be observed in the presence of Candida, reflecting a higher risk of mixed infection. In dermatophyte-positive specimens, the “dermatophytosis complex” variant was observed at 45.5% (SD: 2.3). An analysis of patient characteristics showed male patients exhibiting higher likelihoods for dermatophyte, C. minutissimum, Pseudomonas and S. aureus detections. The elderly were disproportionately infected with Candida. In children, an S. aureus detection was more common, which could be attributed to impetigo. The recent literature lacks reporting on concomitant bacterial colonization in tinea pedis patients, likely due to the reliance on fungal culture supplemented with antibiotics. Geographical variation has been identified in the detection of the Trichophyton mentagrophytes complex. In conclusion, PCR diagnosis serves as a valuable tool for the management of tinea pedis. An accurate and timely detection of fungal pathogens and concomitant bacterial colonization can better inform healthcare providers of appropriate treatment selection

Global Dermatophyte Infections Linked to Human and Animal Health: A Scoping Review

Dermatophytes are commonly encountered pathogens in clinical practice causing superficial infections of the skin, hair, and nails. These pathogens are often found on animals such as livestock (e.g., cattle, rabbits) and pets (e.g., cats, hedgehogs) that can lead to spillover infections in human populations. Here, we reviewed published reports (2009–2024) of dermatophyte infections in animals and in humans with a history of animal contact. A literature search was completed in October 2024 using PubMed, Embase (Ovid), and Web of Science (Core Collection), which identified 250 articles. Generally, dermatophytes tend to infect younger animals with long hair and exhibit a species-specific host range. Microsporum canis was the most commonly reported species—linked to cats—that can cause tinea capitis, especially concerning the development of kerion in children. Trichophyton verrucosum is strongly associated with cattle. The Trichophyton mentagrophytes complex shows a diverse range of animal hosts, with rabbits being most frequently reported; however, T. mentagrophytes var. erinacei is almost exclusively isolated from hedgehogs, and T. mentagrophytes var. benhamiae is more commonly found on rodents (e.g., guinea pigs). Lastly, the geophilic Nannizia gypsea has been isolated from both dogs and cats. Managing dermatophyte zoonoses is an ongoing challenge, as healthcare providers may empirically treat with corticosteroids or antibacterial agents due to its atypical inflammatory appearance. Evidence of in vitro resistance against griseofulvin and fluconazole has been documented in multiple zoonotic dermatophyte species. Resistance development against terbinafine and itraconazole is also a possibility, although the number of reports is scarce. Under the principles of the One Health approach, research on human fungal diseases should take animal and environmental factors into account. A renewed call for increased testing efforts is warranted