CANDIDIASIS 

Candidiasis refers to infections caused by Candida species — opportunistic yeasts that are part of normal human flora.
They can cause disease ranging from superficial mucocutaneous infections to life-threatening disseminated candidemia in immunocompromised or critically ill hosts.


 ETIOLOGY AND MICROBIOLOGY

Common Candida Species

Species

Typical Setting

Key Features

Candida albicans

Most common overall

Germ tube positive; pseudohyphae formation

C. glabrata

Elderly, diabetics, fluconazole exposure

Intrinsically less susceptible to azoles

C. tropicalis

Neutropenic, cancer patients

Frequent bloodstream isolate

C. parapsilosis

TPN, catheter-related infection

Biofilm formation on plastics

C. krusei

Hematologic malignancy

Intrinsically resistant to fluconazole

C. auris

ICU outbreaks

Multidrug resistant; nosocomial spread


 PATHOGENESIS

  • Commensal → Pathogen transition occurs with:
    • Disruption of normal flora (antibiotics)
    • Mucosal barrier breach (catheters, surgery)
    • Immunosuppression (HIV, chemotherapy, steroids)
    • Hyperglycemia, TPN, broad-spectrum antibiotics
  • Virulence factors
    • Adherence to epithelial and plastic surfaces
    • Biofilm formation
    • Phenotypic switching (yeast ↔ hyphae)
    • Secretion of proteinases and phospholipases


 HOST DEFENSE MECHANISMS

  • Innate immunity: Neutrophils and macrophages are critical.
  • Adaptive immunity: Th17 response maintains mucocutaneous integrity.
  • Predisposing factors for invasive disease
    • Neutropenia
    • Central venous catheters
    • Broad-spectrum antibiotics
    • TPN, surgery, ICU stay
    • Immunosuppression, transplantation


 CLASSIFICATION

1. Superficial/Mucocutaneous Candidiasis

  • Oropharyngeal (Thrush)
    • White curd-like plaques on mucosa, scrapable
    • Common in HIV, steroids, diabetes
  • Esophageal Candidiasis
    • Dysphagia, odynophagia
    • Often in AIDS; presumptive diagnosis if thrush + symptoms
  • Vulvovaginal Candidiasis
    • Thick white “cottage cheese” discharge, pruritus, burning
    • C. albicans most common; recurrent form with C. glabrata
  • Cutaneous Candidiasis
    • Intertrigo (moist folds), paronychia, diaper rash
    • Satellite lesions typical
  • Chronic Mucocutaneous Candidiasis (CMC)
    • Associated with T-cell defects, endocrinopathy (APS-1)


2. Invasive/Disseminated Candidiasis

Occurs when Candida enters bloodstream → spreads to organs.

a. Candidemia

  • Most common invasive form.
  • Seen in ICU, neutropenia, TPN, central venous catheter (CVC).
  • May lead to seeding of eyes, liver, spleen, kidney, heart.

 Candida Score (Leon Score)

Used to identify high-risk ICU patients.

Variable

Points

Surgery

1

TPN

1

Multifocal Candida colonization

1

Severe sepsis

2

 Score ≥3 → High risk → Consider empiric antifungal


b. Deep-seated Candidiasis

  • Hepatosplenic Candidiasis – post neutropenia, “bull’s-eye” lesions on CT.
  • Renal Candidiasis – pyelonephritis, fungus balls.
  • Endocarditis – post valve replacement or IVDU.
  • Endophthalmitis – ocular seeding from candidemia.
  • Peritonitis – after surgery or peritoneal dialysis.


 DIAGNOSIS

1. Direct Microscopy

  • KOH mount: budding yeast, pseudohyphae.
  • Gram stain: Gram-positive oval budding yeast.

2. Culture

  • Sabouraud dextrose agar: creamy white colonies.
  • Chromogenic agar: species differentiation (esp. C. auris).
  • Blood culture: gold standard for candidemia (but slow).

3. Non-culture methods

Test

Principle

Notes

β-D-glucan assay

Detects fungal cell wall component

Positive in most fungi (except Cryptococcus, Mucor)

Mannan antigen / Anti-mannan Ab

Candida cell wall markers

Used in combination for improved sensitivity

PCR-based assays

Rapid species ID

May detect before blood culture positivity

4. Imaging

  • CT/MRI: detect hepatosplenic abscesses, renal lesions.
  • Fundus exam: rule out endophthalmitis in all candidemia cases.


 TREATMENT (IDSA 2021 Guidelines)

A. Mucocutaneous Candidiasis

Site

First-line

Alternatives

Oropharyngeal

Topical nystatin or clotrimazole

Oral fluconazole  x 7–14 days

Esophageal

Oral/IV fluconazole  x 14–21 days

Echinocandin or voriconazole if resistant

Vulvovaginal

Topical azoles or oral fluconazole

Boric acid or nystatin for C. glabrata

Cutaneous

Topical clotrimazole, miconazole

Oral fluconazole if extensive


B. Invasive Candidiasis (Candidemia)

Initial therapy

  • Echinocandin (preferred empiric choice):
    • Caspofungin 
    • Micafungin 
    • Anidulafungin 
  • Alternative (stable, no prior azoles): Fluconazole 

Step-down therapy

  • Switch to oral fluconazole once:
    • Clinically stable
    • Isolate susceptible
    • Blood cultures negative for 5–7 days

Duration

  • Minimum 14 days after first negative blood culture and symptom resolution.

Catheter management

  • Remove all central lines if feasible — critical step in management.

Eye examination

  • Mandatory within 1 week of candidemia to exclude ocular seeding.


C. Organ-specific Therapy

Site

Preferred Drug

Duration

Endocarditis

Echinocandin or amphotericin B ± valve replacement

≥6 weeks

Endophthalmitis

Amphotericin B ± flucytosine; intravitreal amphotericin

≥6 weeks

Hepatosplenic

Echinocandin → fluconazole

Several months, until lesion resolution

Urinary Tract

Fluconazole (if susceptible)

2 weeks; remove catheter

CNS

Liposomal amphotericin B + flucytosine

≥6 weeks


 MULTIDRUG-RESISTANT CANDIDA auris

  • Emerging global nosocomial pathogen.
  • Resistant to fluconazole; variable to amphotericin.
  • Preferred: Echinocandins.
  • Strict infection control and environmental decontamination are crucial due to persistence on surfaces.


 PREVENTION AND PROPHYLAXIS

  • Restrict broad-spectrum antibiotics.
  • Limit use of central venous catheters and TPN.
  • Prophylactic fluconazole in high-risk:
    • Bone marrow transplantation
    • Prolonged neutropenia
  • ICU infection control bundles: chlorhexidine baths, line care.


 HIGH-YIELD POINTS FOR EXAMS

  • Germ tube test positive = C. albicans.
  • C. glabrata & krusei → Fluconazole-resistant.
  • Echinocandins → first-line for candidemia.
  • Always remove catheters in candidemia.
  • Ophthalmologic exam in all bloodstream cases.
  • C. auris → multidrug resistant ICU outbreak pathogen.


 REFERENCES

  1. Harrison’s Principles of Internal Medicine, 21st Ed.
  2. IDSA Clinical Practice Guideline for the Management of Candidiasis (2021 update).
  3. Pappas PG, et al. Clin Infect Dis 2021;73(2):e39–e114.
  4. StatPearls: Candidiasis (updated 2025).