Candidiasis

Candidiasis is the general term for opportunistic fungal infections caused by various species of Candida, primarily Candida albicans. Clinical manifestations range from superficial mucocutaneous infections to life-threatening systemic diseases. Infection typically occurs in individuals with compromised immune systems and can affect the mouth, esophagus, vagina, skin, lungs, or the systemic circulation. Candidiasis is also commonly known in the public as “thrush,” “moniliasis,” or “candidosis.”

Candidiasis (generated by artificial intelligence.)

Etiology and Microbiology

The causative agents of candidiasis are species of the genus Candida, which are yeast-like fungi. The most common species is Candida albicans, but other species such as C. glabrata, C. parapsilosis, C. tropicalis, C. krusei, C. lusitaniae, C. kefyr, and more recently, the multidrug-resistant Candida auris which has emerged as a significant health threat, can also cause the disease.

Candida albicans is a component of the normal human microbiota, commonly found as a commensal in the mouth, gastrointestinal tract, vagina, and skin. However, it becomes pathogenic under conditions that suppress the immune system, disrupt microbial balance, or damage mucosal integrity.

Epidemiology

Candidiasis can occur in all age groups but is most common in infants, the elderly, pregnant women, and individuals with compromised immune systems. Approximately 90% of patients with HIV/AIDS develop oral candidiasis. Vaginal candidiasis is a prevalent infection, affecting about 75% of women at least once in their lifetime. An increase in infections caused by non-albicans species has been observed, and the emergence of antifungal resistance in some of these species has made treatment strategies increasingly important.

Clinical Presentations

1. Oral Candidiasis

It is characterized by white, pseudomembranous plaques on the oral mucosa that, when removed, leave behind erythematous areas. There are three main clinical forms:

• Pseudomembranous Candidiasis (Thrush): The most common form, presenting with curd-like plaques on the tongue, buccal mucosa, and palate.
• Erythematous Candidiasis: Develops after prolonged use of broad-spectrum antibiotics or corticosteroids; characterized by papillary atrophy on the central dorsum of the tongue.
• Chronic Hyperplastic Candidiasis: Presents with white, firm, non-removable plaques and carries a premalignant potential.

Other forms include angular cheilitis, median rhomboid glossitis, linear gingival erythema, and denture stomatitis.

2. Vaginal Candidiasis

It is characterized by itching, burning, vulvar erythema, and thick, white, curd-like discharge. Risk factors include diabetes, pregnancy, antibiotic use, and hormonal contraceptives. In chronic or recurrent cases, underlying endocrine disorders should be investigated.

3. Systemic Candidiasis

C. albicans can enter the bloodstream by crossing the gastrointestinal mucosa, adhering to foreign bodies such as catheters, or through invasive procedures. It can lead to forms such as candidemia, endocarditis, meningitis, osteomyelitis, ocular infections, and renal candidiasis. Mortality rates are particularly high in patients with immune deficiency.

4. Candida auris Infections

Candida auris, which has become a major cause of healthcare-associated infections since the 2010s, exhibits high rates of antifungal resistance and significant potential for epidemic spread. Clinical symptoms are nonspecific. It can cause candidemia and other invasive infections. Colonization is common and may occur without symptoms.

Pathogenesis

Candidiasis typically arises when the host defense system is weakened. Candida transitions from its yeast form to its hyphal form, disrupting mucosal integrity. This morphological shift determines the severity of the infection. Other factors influencing the transition from colonization to infection include alterations in mucosal flora, hormonal influences, diabetes, and local hygiene.

Histopathology

Microscopically, sponge-like epidermal changes, neutrophil infiltration, pseudomembrane formation, and hyphal invasion of epithelial cells are observed. For differential diagnosis, Candida yeast and hyphal forms can be visualized using GMS (Gomori Methenamine Silver) and PAS (Periodic Acid-Schiff) stains.

Diagnostic Methods

• Clinical evaluation: Physical examination of oral, vaginal, or skin lesions is often diagnostic.
• Microscopy: Budding yeast and hyphae visible in KOH preparations.
• Culture: Isolation of Candida species on Sabouraud dextrose agar.
• Blood culture: The most important diagnostic tool for systemic candidiasis.
• PCR and MALDI-TOF MS: Modern methods for species identification and resistance analysis.

Treatment

Treatment varies according to the site, severity, and immune status of the patient:

• Superficial candidiasis: Topical antifungals (nystatin, clotrimazole, miconazole).
• Vaginal candidiasis: Single oral dose of fluconazole 150 mg or intravaginal antifungal cream.
• Oral candidiasis: Nystatin suspension, fluconazole tablets, or miconazole oral gel.
• Systemic candidiasis: Fluconazole, echinocandins (caspofungin, anidulafungin), or amphotericin B. Echinocandins are generally first-line for C. auris.

Differential Diagnosis

Pseudomembranous lesions may be confused with other dermatological conditions such as psoriasis, impetigo, tinea infections, and leukoplakia. Microscopy and special stains are essential for differential diagnosis. Laryngeal candidiasis, particularly in women with reflux or using inhaled steroids, can mimic dysphonia.

Complications

Untreated candidiasis may lead to the following complications:

• Systemic dissemination: Sepsis, endocarditis, meningitis.
• Vaginal candidiasis during pregnancy: Low birth weight, neonatal thrush.
• Chronic infections: Particularly in immunocompromised patients.
• Intertrigo: Inflammation occurring between opposing skin surfaces due to Candida.

Prevention and Patient Education

• Vaginal douching, perfumed products, and unnecessary antibiotic use should be avoided.
• Oral hygiene is especially important for individuals using dentures.
• Diabetes control, hygiene, and balanced nutrition are preventive strategies.
• Patients at risk for C. auris should be isolated and infection control measures implemented.

Prognosis

Superficial forms of candidiasis generally have a good prognosis. However, systemic forms can cause high morbidity and mortality. Early diagnosis and appropriate antifungal therapy are critical, especially in immunocompromised patients.

Multidisciplinary Management

In the diagnosis and treatment of candidiasis, infectious disease specialists, dentists, gynecologists, dermatologists, clinical microbiologists, and intensive care specialists should collaborate. Consultations with endocrinology and gastroenterology may be required for chronic or recurrent cases.