Candidiasis - A Complete Guide

What Is Candidiasis?

"Candida albicans is an opportunistic organism, acting as a pathogen in the presence of impaired immune response, or where local conditions favor growth."

• Andrews' Diseases of the Skin

The Organism

• Morphology: Dimorphic - exists as budding yeasts (blastoconidia), pseudohyphae, and true hyphae. The ability to switch between these forms is a key virulence trait.
• Key species: C. albicans is still the single most common, but non-albicans species now collectively account for the majority of invasive disease. The "Big Five" are:
  1. C. albicans
  2. C. glabrata (now Nakaseomyces glabrata)
  3. C. parapsilosis
  4. C. tropicalis
  5. C. krusei (now Pichia kudriavzevii)
• Candidal colonization is found in the oral mucosa of >40% of healthy adults, with higher rates in women and smokers.
• Medical Microbiology 9e

Predisposing Factors

• Medical Microbiology 9e, Table 65.1

Pathogenesis

1. Endogenous translocation - normal commensal flora breaches a disrupted epithelial barrier
2. Exogenous transmission - contaminated catheters, IV fluids, or hospital environment

• Adhesins (adhere to epithelial and endothelial cells)
• Hydrolytic enzymes (proteases, phospholipases)
• Phenotypic switching
• Biofilm formation on catheters and prosthetic devices
• The IL-17 pathway is the primary immunological defense; defects in this pathway predispose to mucocutaneous candidiasis

Types of Candidiasis

A. MUCOCUTANEOUS CANDIDIASIS

1. Oropharyngeal Candidiasis (Oral Thrush)

Angular cheilitis - erythema and scaling at the oral commissures

2. Esophageal Candidiasis

• The most common cause of infectious esophagitis
• Presents with odynophagia (painful swallowing), dysphagia, and retrosternal discomfort
• Strongly associated with AIDS (CD4 < 100), and also hematologic malignancies
• Diagnosis: Endoscopy shows white plaques with erythematous base; brushings show pseudohyphae on KOH
• Always requires systemic (not just topical) treatment - fluconazole 200 mg/day for 14 days is the standard

3. Vulvovaginal Candidiasis (VVC)

• Affects ~75% of women at least once in their lifetime; 5-8% have recurrent VVC (≥4 episodes/year)
• Symptoms: intense vulvar itching, burning, external dysuria, thick white "cottage cheese" discharge
• The vaginal pH is normal (<4.5) - this distinguishes it from bacterial vaginosis and trichomonas
• Uncomplicated VVC: short-course topical azoles (clotrimazole, miconazole) or single-dose oral fluconazole 150 mg
• Recurrent VVC: suppressive fluconazole therapy; newer agents - oteseconazole, ibrexafungerp
• Self-diagnosis is frequently incorrect - laboratory confirmation improves accuracy

4. Cutaneous Candidiasis (Candidal Intertrigo)

• Axillae, inguinal folds, inframammary creases
• Perianal region, abdominal skin folds
• Interdigital spaces (especially 3rd web space - "erosio interdigitalis blastomycetica")
• Diaper area in infants

Typical cutaneous candidiasis: erythematous plaques coalescing with satellite papules and vesiculopustules (Fitzpatrick's Dermatology)

5. Candidal Diaper Dermatitis

• Common in infants - the moist, occluded environment of diapers is ideal for growth
• Presents as beefy-red plaques with satellite pustules in the diaper area
• Unlike simple irritant diaper rash, it involves the skin folds (not just the convex surfaces)
• Treat with topical nystatin or clotrimazole + frequent diaper changes

6. Candidal Paronychia and Onychomycosis

• Chronic paronychia: erythematous, swollen, tender proximal nail fold - loss of the cuticle is a hallmark
• Affects people with repeated wet-work exposure (dishwashers, bartenders, healthcare workers)
• Onychomycosis follows if the infection spreads to the nail plate - thickening, discoloration, onycholysis
• Treatment: topical ciclopirox or systemic fluconazole/itraconazole

7. Balanitis / Balanoposthitis

• Candidal infection of the glans penis and prepuce
• Presents with erythema, edematous papules, pustules, and white discharge under the foreskin
• Risk factors: uncircumcised males, diabetes, sexual contact with infected partner
• Pustules are more characteristic here than in vulvitis

8. Chronic Mucocutaneous Candidiasis (CMC)

• Onset often in childhood
• Nails and skin can develop thick, verrucous, hyperkeratotic plaques ("candida granuloma")
• Requires lifelong suppressive azole therapy (fluconazole 200-400 mg daily)

Chronic mucocutaneous candidiasis: sharply marginated erythematous plaques with prominent scaling, resembling plaque psoriasis (Fitzpatrick's Dermatology)

B. INVASIVE (SYSTEMIC) CANDIDIASIS

9. Candidemia (Bloodstream Infection)

• The 4th most common cause of nosocomial bloodstream infection in the US
• Classic triad: fever + rash + myalgia in a hospitalized patient
• Skin lesions appear in 10-30% of cases - sparse erythematous papules with central pallor/necrosis on the trunk and proximal extremities; most commonly associated with C. tropicalis
• All patients with candidemia must be treated - even a single positive blood culture warrants therapy (due to high rate of metastatic foci)
• Vascular catheters should be removed when feasible

Disseminated candidiasis in a neutropenic patient with AML: erythematous papules and nodules on the hand with central pustulation; blood cultures positive for C. tropicalis (Fitzpatrick's Dermatology)

• ICU stay, broad-spectrum antibiotics
• Central venous catheters, TPN
• Hematologic malignancy, neutropenia
• Abdominal surgery, organ transplant
• Hemodialysis, extreme prematurity

10. Chronic Disseminated Candidiasis (Hepatosplenic Candidiasis)

• Occurs in patients recovering from prolonged neutropenia (often after chemotherapy)
• Paradoxically develops as neutrophils recover
• Presents with persistent fever despite antibiotic therapy, right upper quadrant pain, elevated ALP
• CT/MRI shows multiple small "bullseye" lesions in liver and spleen
• Requires prolonged antifungal therapy (months)

11. Candida Endocarditis

• Rare but highly lethal (~50% mortality)
• Associated with IV drug use, prosthetic heart valves, prolonged central catheters, prior cardiac surgery
• Large bulky vegetations on aortic/mitral valves
• Large emboli to major arteries (femoral, iliac) are a hallmark
• Requires antifungal therapy + surgical valve replacement in most cases

12. Candida Meningitis / CNS Candidiasis

• Uncommon; seen in very low birth weight neonates, post-neurosurgical patients, HIV/AIDS
• CSF: elevated protein, low glucose, pleocytosis
• Echinocandins have poor CNS penetration - use liposomal amphotericin B ± flucytosine, then fluconazole for consolidation

13. Candida Urinary Tract Infection

• Candiduria is common in catheterized, hospitalized patients - most cases are asymptomatic colonization
• Symptomatic cystitis/pyelonephritis is rare and typically seen in diabetics, patients with anatomic abnormalities
• Treatment of asymptomatic candiduria is NOT recommended (except before urologic procedures or in neutropenic/transplant patients)
• Fluconazole is first-line for symptomatic disease (echinocandins have poor urinary excretion)

14. Candidal Osteomyelitis / Osteoarthritis

• Hematogenous seeding to bone or joints - most commonly vertebrae
• IV drug users are at risk for candidal arthritis (large joints: knee, hip)
• Requires prolonged antifungal therapy ± surgical debridement

Diagnosis Summary

Treatment Overview

Quick Memory Map

CANDIDIASIS
├── MUCOCUTANEOUS (superficial)
│   ├── Oral → Thrush / Erythematous / Hyperplastic / Angular cheilitis
│   ├── Esophageal → Odynophagia, AIDS-defining
│   ├── Vulvovaginal → Cottage-cheese discharge, normal pH
│   ├── Cutaneous (Intertrigo) → Beefy-red + satellite pustules
│   ├── Diaper rash → Involves skin folds
│   ├── Paronychia / Onychomycosis → Wet-work exposure
│   ├── Balanitis → Uncircumcised + diabetics
│   └── Chronic Mucocutaneous (CMC) → IL-17 defect, lifelong therapy
│
└── INVASIVE (systemic)
    ├── Candidemia → ICU, catheters, fever+rash+myalgia
    ├── Hepatosplenic → Post-neutropenia recovery, bullseye lesions
    ├── Endocarditis → Large vegetations, IVDU, prosthetic valves
    ├── Meningitis → Neonates, post-neurosurgery
    ├── UTI → Catheterized patients, usually colonization
    └── Osteomyelitis/Arthritis → Vertebrae, IVDU