Describe candidiasis with its predisposing factors, clinical forms, laboratory diagnosis and treatment.

The Organism

• Candida albicans is the commonest species, but non-albicans species are increasing — C. Glabrata, C. Tropicalis, C. Parapsilosis, C. Krusei and C. Auris
• A yeast-like fungus — oval budding cells with pseudohyphae, and true hyphae in invasive disease. It forms smooth creamy colonies on Sabouraud agar
• A normal commensal of the mouth, gastrointestinal tract and vagina in a large proportion of healthy people — so infection is nearly always endogenous, arising when the balance shifts rather than on acquisition from outside
• Virulence factors — adhesins; the yeast-to-HYPHA transition, which is required for tissue invasion; secreted aspartyl proteases and phospholipases; biofilm formation on catheters and prostheses; and phenotypic switching

Predisposing Factors

Clinical Forms

Laboratory Diagnosis

• Microscopy — Gram stain or KOH mount showing budding yeasts with pseudohyphae. In tissue, seeing hyphae indicates invasion, whereas yeasts alone may represent colonisation
• Culture on Sabouraud agar at 37°C, giving creamy colonies within 24 to 48 hours; CHROMagar distinguishes species by colony colour, which matters because species predicts susceptibility
• Germ tube test (Reynolds-Braude phenomenon) — incubation in serum at 37°C for 2 to 3 hours produces germ tubes without a constriction at the point of origin, identifying C. Albicans and C. Dubliniensis rapidly and cheaply
• Chlamydospore formation on cornmeal agar with Tween 80 — thick-walled terminal chlamydospores are characteristic of C. Albicans
• Sugar assimilation and fermentation, automated identification systems, and MALDI-TOF
• Blood culture is positive in only about 50% of invasive candidiasis, so a negative result does not exclude it; beta-D-glucan and T2Candida assays and PCR help in that gap
• Interpretation is the difficulty — because Candida is a commensal, isolating it from sputum, a wound swab or catheter urine usually means colonisation, and only isolation from a normally sterile site proves infection

Differentiating the Candida Species

Treatment and Applied Aspects

• Topical for mucocutaneous disease — nystatin, clotrimazole or miconazole; oral fluconazole for oesophageal, recurrent or extensive disease
• Invasive candidiasis — an echinocandin (caspofungin, micafungin, anidulafungin) is first-line, being fungicidal, well tolerated and active against most species; fluconazole where the isolate is susceptible and the patient stable; liposomal amphotericin B as an alternative
• Species predicts resistance — C. Krusei is intrinsically resistant to fluconazole, C. Glabrata is often resistant or dose-dependent, and C. Parapsilosis has reduced echinocandin susceptibility — so identification to species level directly changes treatment
• Remove the central line in candidaemia; biofilm on the catheter cannot be sterilised, and retention is associated with persistent fungaemia and death
• Perform fundoscopy in every case of candidaemia to detect endophthalmitis, which is sight-threatening and requires prolonged and different treatment; and take repeat blood cultures to document clearance
• Do not treat asymptomatic candiduria in a catheterised patient; remove or change the catheter instead
• Look for the underlying cause — check the blood glucose, review the antibiotics and steroids, and consider HIV; treating the candidiasis without addressing the reason for it guarantees recurrence
• Seeing hyphae in tissue indicates invasion, whereas yeasts alone may be colonisation — a distinction the histopathology report should be asked for explicitly
• Rinse the mouth after an inhaled corticosteroid and use a spacer; oral candidiasis in an asthmatic is usually a technique problem rather than an immune one
• Oesophageal candidiasis is AIDS-defining, and its diagnosis in an adult should prompt HIV testing without exception
• Vaginal candidiasis has a normal pH, unlike bacterial vaginosis and trichomoniasis; a simple pH strip separates the three at the bedside and avoids inappropriate treatment
• Candidaemia mortality is high and time-dependent, so empirical antifungal treatment is started in a septic patient with risk factors rather than awaiting culture
• Non-albicans species now account for about half of isolates in many Indian units, which is why species identification cannot be treated as an academic refinement
• C. Parapsilosis is carried on the hands of staff and grows in parenteral nutrition, so hand hygiene and line care are the specific preventive measures in neonatal units
• Repeat blood cultures until they are negative, and count the duration of treatment from the first negative culture rather than from the start of therapy
• Do not treat Candida grown from sputum; it essentially never causes pneumonia in an immunocompetent adult and represents oropharyngeal contamination