Fungal Infections — Candidiasis & Dermatophytes

A healthy adult walks into the clinic with oral thrush and no recent antibiotic use — before you reach for the nystatin, ask yourself what immunodeficiency you might be about to diagnose.

Candidiasis: Candida albicans is an opportunistic yeast that normally colonizes the skin, GI tract, and vaginal mucosa. Overgrowth occurs when normal flora is disrupted or immunity is impaired. Oral thrush presents as white adherent plaques on the tongue, buccal mucosa, and palate that bleed when scraped. Risk factors: antibiotic use (disrupts competing flora), corticosteroid inhaler use (always teach patients to rinse mouth after inhaled corticosteroids), immunosuppression (HIV/AIDS, chemotherapy), diabetes, denture use, and extremes of age (neonates and elderly). Treatment: mild thrush may be treated with topical nystatin suspension (swish and swallow) or clotrimazole troches; fluconazole is used for moderate/severe disease, immunocompromised patients, or refractory cases. Vaginal candidiasis: thick white cottage-cheese-like discharge with pruritus and erythema; no odor. Risk factors: antibiotics, pregnancy, diabetes, oral contraceptives. Treatment: fluconazole 150 mg single oral dose or topical azole (miconazole, clotrimazole). Invasive candidiasis: bloodstream infection primarily in ICU patients with central venous catheters, broad-spectrum antibiotics, TPN, or abdominal surgery. Treatment: echinocandins (caspofungin, micafungin) first-line, remove central line. Dermatophytes (tinea): superficial fungal infections of keratinized tissue. Tinea capitis (scalp — children primarily, patches of hair loss with scaling), tinea corporis (body — annular ring-shaped lesion with raised border and central clearing, commonly called 'ringworm'), tinea pedis (feet — interdigital maceration, scaling, pruritus, 'athlete's foot'), tinea cruris (groin — bilateral red patches in inguinal folds, 'jock itch'), tinea unguium/onychomycosis (nails — thickened, discolored, brittle). Diagnosis: KOH preparation (dissolves skin cells, reveals fungal hyphae under microscopy), Wood lamp fluorescence (some species). Treatment: topical antifungals (clotrimazole, terbinafine) for skin infections; oral terbinafine or griseofulvin for scalp and nail infections (topical alone does not penetrate). Nursing: keep affected areas clean and dry, complete full treatment course, educate that 'ringworm' is a fungus not a worm, do not share personal items, and wear shower shoes in communal areas.

Key Distinctions

Oral thrush in an otherwise healthy adult without recent antibiotic use should prompt HIV testing — this is a high-yield clinical pearl frequently tested on NCLEX. Vaginal candidiasis produces thick white odorless discharge; bacterial vaginosis produces thin gray fishy-smelling discharge; trichomoniasis produces frothy green-yellow discharge — the discharge characteristics differentiate the three. Tinea capitis and onychomycosis require oral antifungals because topical agents cannot penetrate hair follicles or the nail plate. Do not confuse tinea corporis (ring-shaped, fungal) with nummular eczema (coin-shaped, inflammatory) — KOH prep differentiates them.

Clinical Pearl

Thrush in a healthy adult with no obvious cause — test for HIV. The mouth is often the first place immunodeficiency shows itself.