10.3 Candidiasis & Fungal Infections
Key Takeaways
- Candida albicans is a commensal that becomes pathogenic under predisposing factors — xerostomia, antibiotics, steroids, denture wearing, immunosuppression, iron/B12/folate deficiency, diabetes, and HIV
- The five clinical forms are pseudomembranous (thrush), erythematous (antibiotic sore mouth and denture-related), angular cheilitis, chronic hyperplastic (candidal leukoplakia, premalignant), and median rhomboid glossitis
- Miconazole oral gel carries a clinically significant interaction with warfarin (inhibits metabolism, raising INR and bleeding risk) — avoid in warfarinised patients and use nystatin or systemic fluconazole instead
- Management requires addressing the predisposing cause plus topical antifungal (nystatin or miconazole) for localized disease and systemic fluconazole for resistant or immunocompromised patients
- Denture hygiene is core prevention: remove dentures overnight and soak them in chlorhexidine to reduce Candida colonisation of the fitting surface
The Organism
Candida albicans is a dimorphic yeast carried asymptomatically in the oral cavity by roughly half the adult population. It is a commensal turned opportunist: disease arises only when local or systemic host defences are disrupted.
Predisposing Factors (the 7 Cs and more)
| Local | Systemic |
|---|---|
| Denture wearing (especially at night) | Broad-spectrum antibiotics |
| Xerostomia (drugs, Sjogren, radiotherapy) | Corticosteroids (inhaled and systemic) |
| Smoking | Immunosuppression (HIV, chemotherapy, transplant) |
| High-carbohydrate diet | Iron, vitamin B12, folate deficiency |
| Poor oral hygiene | Diabetes mellitus |
| Inhaler use without rinsing | Pregnancy, extremes of age |
The mnemonic commonly taught is that any factor altering oral flora, saliva flow, or immune competence can tip the balance toward candidiasis.
Clinical Forms
| Form | Appearance | Key feature |
|---|---|---|
| Pseudomembranous (thrush) | White, creamy plaques that wipe off leaving erythematous base | Classic, seen in infants, immunosuppressed, antibiotic users |
| Erythematous | Red, atrophic patch; sore burning mucosa | Antibiotic sore mouth; denture-related (under the denture) |
| Angular cheilitis | Cracked, erythematous commissures | Often with dentures, iron deficiency, or S. aureus co-infection |
| Chronic hyperplastic (candidal leukoplakia) | Fixed white plaque that does not wipe off | Premalignant — needs biopsy; usually anterior buccal mucosa |
| Median rhomboid glossitis | Lozenge-shaped erythema mid-dorsal tongue | Often asymptomatic; denture wearers; Candida on biopsy |
The wipeable / non-wipeable distinction is the single most useful clinical discriminator: pseudomembranous candidiasis wipes off, chronic hyperplastic candidiasis (and idiopathic leukoplakia) do not, and biopsy is required to separate the latter two.
Diagnosis
- Smear with potassium hydroxide (KOH) — rapid; shows hyphae and budding yeast
- Swab for culture — confirms species and antifungal sensitivities
- Biopsy — only for chronic hyperplastic lesions to exclude dysplasia (candidal leukoplakia is premalignant)
- Consider baseline bloods (FBC, ferritin, B12, folate, HbA1c, HIV test if risk) to identify predisposing causes
Management
Step 1 — Address the predisposing cause
Stop unnecessary antibiotics, optimise diabetes, treat iron/B12/folate deficiency, rinse after using steroid inhalers, improve denture hygiene. Treating the cause alone often resolves mild candidiasis.
Step 2 — Topical antifungal
| Agent | Form | Dose |
|---|---|---|
| Nystatin | Oral suspension 100,000 units/mL | 1 mL qds, swish and swallow, 7-14 days |
| Miconazole | Oral gel 2% (Daktarin) | 2.5 mL qds, hold in mouth |
| Amphotericin | Lozenges/suspension | 10 mg qds |
Safety alert: Miconazole oral gel inhibits warfarin metabolism (CYP2C9), rapidly raising INR and causing serious bleeding. The MHRA has issued repeated warnings. In any patient taking warfarin, avoid miconazole oral gel and use nystatin or systemic fluconazole instead, with INR monitoring.
Step 3 — Systemic antifungal
Fluconazole 50-100 mg daily for 7-14 days is first-line systemic therapy for:
- Oropharyngeal candidiasis resistant to topical therapy
- Immunocompromised patients (HIV, chemotherapy)
- Severe or widespread disease
Itraconazole or posaconazole are alternatives in resistant or fluconazole-refractory disease (common in late HIV). Always check for drug interactions — fluconazole also interacts with warfarin, statins, and many anticonvulsants.
Denture Hygiene
Dentures are the single biggest reversible risk factor. Counsel every denture patient:
- Remove dentures overnight — Candida thrives in the warm, acidic, low-oxygen space beneath a denture; leaving dentures out at night allows the mucosa to recover
- Clean daily with a brush and soap (not toothpaste — scratches acrylic) and soak in chlorhexidine or a proprietary denture cleanser
- Rinse and brush the palate with chlorhexidine mouthwash
- Replace poorly fitting dentures
Denture-related erythematous candidiasis resolves only when the denture is left out and disinfected, even with antifungal treatment.
Angular Cheilitis
Treat with topical miconazole or clotrimazole cream to the commissures (only if not warfarinised for miconazole), plus address underlying iron deficiency and denture support. If S. aureus is present (culture), add topical fusidic acid.
Non-Albicans Candida and Resistance
Although Candida albicans causes most oral candidiasis, non-albicans species are increasingly recognised and alter management:
| Species | Significance |
|---|---|
| C. glabrata | Often fluconazole-resistant; needs culture and sensitivities |
| C. krusei | Intrinsically fluconazole-resistant; use amphotericin or itraconazole |
| C. tropicalis | Variable susceptibility; can be invasive in neutropenia |
| C. dubliniensis | Associated with HIV; often misidentified as C. albicans |
Refractory or recurrent candidiasis, particularly in the immunocompromised, should prompt culture with species identification and antifungal sensitivities rather than empirical escalation.
When Oral Candidiasis Signals Systemic Disease
New, persistent, or extensive candidiasis in an adult with no obvious local cause is a red flag. Investigate:
- HIV testing - oral candidiasis is common in advanced immunosuppression and oesophageal disease is AIDS-defining; consider it when thrush is recurrent, extensive, or in a high-risk group.
- Diabetes - HbA1c or fasting glucose; poorly controlled diabetes impairs neutrophil function.
- Iron, vitamin B12, and folate deficiency - baseline bloods.
- Malignancy or haematological disease - especially with new-onset thrush in older adults.
Deep Fungal Infections
In profoundly immunocompromised patients (neutropenia, transplant, advanced HIV), invasive fungi may ulcerate the oral mucosa: histoplasmosis produces nodular or ulcerated lesions and is diagnosed by biopsy and culture, while mucormycosis causes a necrotic palatal ulcer, is angioinvasive, and is linked to diabetic ketoacidosis. These are rare but must be considered in a non-healing ulcer in an immunocompromised host.
A 70-year-old warfarinised patient with an INR target range for atrial fibrillation develops oral thrush. Which topical antifungal is contraindicated because of a serious drug interaction?
A 60-year-old denture wearer has a fixed, non-wipeable white plaque on the anterior buccal mucosa that has been present for eight weeks. What is the correct diagnosis and management?
A 55-year-old asthmatic using a beclometasone inhaler for years develops sore erythematous mucosa with white patches. What single preventive measure most directly reduces this complication?
A 40-year-old HIV-positive patient has widespread oral thrush that has not responded to two weeks of nystatin. What is the most appropriate next-line treatment?