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INTRODUCTION

KEY POINTS

  • Fungal infections affect people of all races.

  • Susceptibility to fungal infection is influenced by a variety of factors including socioeconomic status, geographic location, and cultural or religious practices.

  • Dermatophytes cause most superficial fungal infections.

  • In the immunocompromised host, nondermatophyte molds and yeasts are also cutaneous pathogens.

Fungi are ubiquitous worldwide, and cutaneous fungal infections are common among most races.1 Keratinized tissues including stratum corneum, nails, and hair are an adaptive substrate for the superficial mycoses, such as dermatophytes, which are the primary causative agent of fungal infections. The immune system generally provides adequate defense against fungal invasion; consequently, nondermatophyte molds and yeasts are more common in those with primary or secondary immunodeficiency.

The presence of cutaneous mycoses does not appear to be a reflection of differences in the biologic characteristics of skin color. However, underlying immunologic diseases such as human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) are of epidemic proportions in Africa, and studies in this region have identified higher incidences of associated fungal infections.2 Climatic differences affect the ability of fungi to grow; high ambient temperature and humidity provide an ideal setting for fungal proliferation. Additional factors such as occlusive clothing and footwear worn in cooler settings may provide suitable microclimates for mycotic activity. Cultural or religious customs, such as communal bathing, may create opportunities for the transmission of fungi. Variation in hygienic practices also may explain increased susceptibility to fungal invasion.

This chapter provides an overview of superficial fungal infections that are common to most skin types, including individuals with skin of color. Tinea capitis and seborrheic dermatitis, which are covered in detail in Chapters 84 and 23, are fungal infections found more frequently in people with skin of color.

MYCOLOGIC EXAMINATION

Accurate diagnosis of a fungal infection is necessary before selecting an appropriate treatment regimen. Mycologic methods are similar for most mycoses, the goal being confirmation of the presence of fungi and identification of the pathogenic species. Light microscopy and fungal culture are used to determine whether fungal organisms are present in the specimen evaluated. Direct examination is performed using 10% to 20% potassium hydroxide (KOH) to dissolve the surrounding keratin. In addition, calcofluor white or periodic acid–Schiff (PAS) stain may be added to the KOH preparation to enhance visibility of the fungal organism.3,4 The KOH test can indicate the presence or absence of a fungal element but does not give information as to the type of fungal element detected. Due to sampling error and nonproliferating fungi that may not be visible on microscopic examination, a negative microscopic result is not necessarily indicative of fungus-free tissue. A KOH result revealing septate hyphae in the setting of clinical suspicion of fungal infection may be sufficient to initiate treatment. Biopsy is generally not required. Because antifungal agents have different spectra of activity, organism identification ...

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