A 58-year-old man with acute leukemia undergoing chemotherapy develops persistent oral white plaques that do not scrape off easily. Culture on Sabouraud dextrose agar grows Candida species. Which Candida species is the most common cause of oral candidiasis in immunocompromised patients?

Explanation

## Most Common Cause of Oral Candidiasis in Immunocompromised Hosts **Key Point:** Candida albicans is the most frequent cause of oral candidiasis (thrush) across all patient populations, including immunocompromised individuals, accounting for >90% of cases. ### Candida Species Distribution in Oral Infections | Candida Species | Frequency in Oral Candidiasis | Clinical Presentation | Typical Host | |---|---|---|---| | **C. albicans** | >90% | Pseudomembranous thrush, erythematous patches, angular cheilitis | Immunocompromised, antibiotic use, denture wearers | | C. glabrata | 3–5% | Atrophic candidiasis, chronic erythema | Recurrent infections, older patients | | C. parapsilosis | 1–2% | Rare in oral cavity; more common in bloodstream infections | Indwelling catheters, parenteral nutrition | | C. auris | <1% | Nosocomial oral colonization | ICU patients, healthcare-associated | **High-Yield:** In any immunocompromised patient (HIV/AIDS, chemotherapy, organ transplant, corticosteroid use) presenting with oral white plaques or erythema, assume C. albicans until proven otherwise. ### Pathogenesis in Immunocompromised States 1. **Loss of cell-mediated immunity:** CD4+ T-cell depletion (HIV, chemotherapy) removes primary defense against Candida 2. **Disrupted oral flora:** Broad-spectrum antibiotics eliminate competing bacteria, allowing Candida overgrowth 3. **Virulence activation:** Hyphal formation and protease secretion increase in immunosuppressed hosts 4. **Candida albicans specificity:** Superior adhesion to oral epithelium via adhesins (Als proteins) and ability to form biofilms **Clinical Pearl:** Oral candidiasis in a previously healthy adult without obvious immunosuppression (e.g., no HIV, no recent antibiotics) should prompt investigation for underlying malignancy, diabetes, or undiagnosed HIV infection. **Warning:** Do not confuse oral candidiasis with oral hairy leukoplakia (caused by Epstein–Barr virus, not Candida) — hairy leukoplakia does not scrape off, whereas pseudomembranous candidiasis does. **Mnemonic:** **THRUSH** risk factors for oral candidiasis: - **T**. Transplant recipients - **H**. HIV/AIDS (CD4 <200) - **R**. Recent antibiotics - **U**. Underlying malignancy (chemotherapy) - **S**. Steroids (systemic) - **H**. Hyposalivation (xerostomia) [cite:Jawetz, Melnick & Adelberg's Medical Microbiology 28e Ch 45]