Candidiasis

Meet the patient

A 54-year-old woman with type 2 diabetes returns for the fourth time in a year with an itchy, sore, bright-red rash under her breasts and in her groin, edged with tiny pustules that have crept beyond the margin. "It keeps coming back," she says, "and the cream only works for a week."[1][2]

Two questions decide her care, and both recur across every form of candidiasis: what upset the balance that let a commensal become a pathogen? (her diabetes, her folds, her moisture), and why does it keep relapsing? (a cause left uncorrected, or a biofilm she cannot clear). Answer those two and the ladder writes itself.[1]

Why a commensal becomes a pathogen

Candida lives harmlessly on skin, in the mouth, gut and vagina from early infancy. Disease is never the yeast arriving — it is the equilibrium breaking. The disturbances fall into a short, memorable list: moisture and occlusion, lost bacterial flora, high glucose, impaired immunity, and inherited Th17 defects. Recognising which one is at work is usually the key to stopping recurrence.[1][12]

[1] [12]

Local factors are the commonest and the most modifiable. Moisture and occlusion raise local pH, macerate the stratum corneum and strip its mechanical barrier; obesity deepens and widens the folds, and incontinence, sweating, tight synthetics and poor hygiene all pile on. Napkin dermatitis is almost always irritant contact dermatitis with secondary candidal overgrowth, because a warm wet occlusive nappy is a perfect culture plate.[13]

Systemic factors do the same job from the inside. Diabetes impairs neutrophil chemotaxis and phagocytosis and spills glucose into urine and skin; HIV makes oral and oesophageal candidiasis classic opportunistic infections as the CD4 count falls below 200; broad-spectrum antibiotics clear lactobacilli and let Candida bloom; pregnancy and oestrogen raise vaginal glycogen; corticosteroids and IL-17 or TNF biologics blunt antifungal immunity.[3][6]

The species that matter — and the one that scares infection control

Most superficial disease is Candida albicans, but the non-albicans species change the drug choice, so name them. C. glabrata is notable for reduced fluconazole susceptibility; C. tropicalis and C. parapsilosis dominate hospital and catheter-related infections; C. krusei is intrinsically fluconazole-resistant; and Candida auris is the multidrug-resistant, outbreak-prone nosocomial threat that demands isolation and susceptibility testing.[9][10]

Pathophysiology — yeast, hyphae, and the Th17 shield

Candida is dimorphic. As a commensal yeast it is benign; under permissive cues — temperature, pH, nutrients, epithelial contact — it switches to pseudohyphal and hyphal forms that invade tissue, resist phagocytosis and build biofilms. Hyphae are not a shape change but a virulence trait, and the transition is what turns colonisation into disease.[12]

The host defence that holds the line is the Th17 axis — interleukin-17, IL-22 and IL-23 driving neutrophils and epithelial defences at the mucocutaneous surface. When that axis fails, candidiasis becomes persistent and recurrent from infancy. The single most important inherited defect is STAT1 gain-of-function, which hyperphosphorylates STAT1, suppresses IL-17, and produces chronic mucocutaneous candidiasis often joined by endocrine autoimmunity.[8][12]

The clinical signs are the inflammation made visible. Neutrophils mass around invading hyphae to produce the satellite pustules; in the mouth, epithelial hyperplasia and microabscesses produce the white pseudomembranous plaques of thrush. The same mechanisms explain why anyone with barrier disruption, altered flora or defective Th17 immunity is vulnerable — and why they relapse when treatment stops.[1]

The clinical pictures — by site

Cutaneous candidiasis

Candidal intertrigo is the prototypical cutaneous form and the one examiners reach for. Look for a bright-red, moist, shiny, well-demarcated plaque in a skin fold, with a scalloped or collarette edge and the tell-tale satellite pustules or papules scattered just beyond the margin. Itch, burn, soreness and malodour drive the presentation; common sites are the submammary folds, axillae, infrabdominal pannus, inguinal creases, perineum and interdigital toe webs.[1]

Interdigital infection — erosio interdigitalis blastomycetica — macerates and fissures the finger webs of people whose hands stay wet. Napkin candidiasis layers onto irritant napkin dermatitis as a beefy-red confluent eruption that, unlike pure irritant dermatitis, involves the folds and carries satellite pustules — the inversion that earns the mark.[13]

Mucosal candidiasis

Oral thrush wears several masks. Pseudomembranous thrush is the classic: creamy white plaques that scrape off an erythematous, bleeding base, common after antibiotics, inhaled corticosteroids and immunosuppression. Erythematous (atrophic) disease gives a red, burning mucosa without plaques and overlaps with denture stomatitis. Chronic hyperplastic candidiasis gives firm white plaques that will not wipe off and carries a risk of malignant change.[3]

Vulvovaginal candidiasis brings intense vulval itch, soreness, dyspareunia, external dysuria and a non-offensive creamy or curdy white discharge, with vulval erythema, oedema and labial satellite pustules; symptoms peak pre-menstrually. Candidal balanitis gives erythematous papules and plaques on the glans and prepuce, favouring uncircumcised men and diabetes. Angular cheilitis — sore, fissured, macerated commissures — is usually multifactorial, blending Candida, staphylococci, moisture pooling and nutritional deficiency.[6][16]

Nail and peri-ungual disease

Chronic candidal paronychia is the classic nail story, and it is not primarily an infection. The primary problem is irritant contact dermatitis from wet work, with secondary candidal colonisation and episodic bacterial flares. The nail fold is boggy and erythematous, the cuticle is lost, and the plate shows transverse ridging and Beau lines. It haunts barbers, hairdressers, cleaners, cooks, dental and healthcare workers and swimmers — and it is distinguished from acute bacterial paronychia by its chronic, multifinger, low-pain course and cuticle loss rather than pus lifting the fold.[14]

Chronic mucocutaneous candidiasis

When candidiasis is relentless from infancy, look for the immune defect. Chronic mucocutaneous candidiasis (CMC) is persistent, widespread, treatment-resistant disease of skin, nails and mucosa beginning in early childhood, sometimes disfiguring with hyperkeratotic plaques on the face, scalp and hands. The clue is the lifelong, mucocutaneous-restricted pattern — distinct from the episodic, infection-related pattern of HIV. Associated endocrine autoimmunity (hypoparathyroidism, hypothyroidism, adrenal insufficiency) in APECED, dental enamel hypoplasia and nail dystrophy complete the picture.[8][15]

Differential diagnosis — and the bedside framework for a red fold

A red rash in a skin fold has many causes, and a single KOH slide usually settles it. Run three questions: is it scaly and annular with central clearing (tinea corporis)? Is it smooth, well-demarcated and without satellites (inverse psoriasis)? Does it fluoresce coral-red under Wood's lamp (erythrasma)? Three "no" answers plus moist shiny erythema with satellites points to candidal intertrigo.[1][2]

The satellite pustule is the bedside sign worth teaching. A tiny pustule sitting just beyond the edge of a red, moist fold plaque is highly suggestive of candidiasis and is not seen in inverse psoriasis or dermatophyte infection. A Wood's lamp then separates the mimics: erythrasma glows coral-red, pityriasis versicolor copper-orange, and Candida does not fluoresce.[1]

When to suspect something deeper. Severe or recurrent oral candidiasis in an adult without a local cause should trigger HIV and diabetes testing; recurrent vulvovaginal candidiasis should prompt fasting glucose or HbA1c; refractory chronic paronychia should screen for diabetes and, if stubborn, HIV and iron studies; candidiasis from infancy with endocrine signs should raise APECED or CMC.[3][6]

Investigations — KOH first, culture when it will not behave

KOH microscopy is the cornerstone, and the pseudohyphae are the finding that earns the mark. A skin scraping, nail-fold swab or mucosal smear in 10 percent potassium hydroxide shows ovoid budding yeast cells and elongated pseudohyphae strung together like links of sausage. Dermatophytes, by contrast, show branching septate hyphae with no yeast forms — and that single distinction sets therapy, because terbinafine works for tinea but generally not for Candida.[1]

[1]

Reserve culture for the awkward case — atypical, recurrent, refractory, severe disease, or when species identification matters. Sabouraud agar or CHROMagar gives presumptive species ID, and antifungal susceptibility testing is essential for Candida auris, C. glabrata and C. krusei, and for any therapy failure. Send blood cultures whenever invasive disease is suspected, and arrange endoscopy for oesophageal candidiasis that is uncertain or refractory. For recurrent or unusual disease, screen the predisposing conditions: fasting glucose or HbA1c, HIV Ag/Ab, iron studies, and — when CMC or APECED is on the cards — a calcium, phosphate, parathyroid hormone, thyroid, cortisol and ACTH panel, with genetics arranged by immunology.[7][9]

Resuscitation — when candidiasis is not a skin problem

The life-threatening form is candidemia or invasive candidiasis, not the intertrigo. The triggers are indwelling lines, broad-spectrum antibiotics, parenteral nutrition, prolonged ICU stay, immunosuppression, GI surgery and haematological malignancy; the presentation is persistent fever, hypotension, sepsis and positive blood cultures. The IDSA 2016 guideline makes an echinocandin first-line for candidemia in the non-neutropenic adult — caspofungin 70 mg loading then 50 mg intravenously daily, micafungin 100 mg intravenously daily, or anidulafungin 200 mg loading then 100 mg intravenously daily. [7][9]

Source control matters as much as the drug. Remove the infected central line whenever feasible — persistent candidemia is far more likely if it stays. Drain any abscess, and arrange ophthalmology review to exclude candidal endophthalmitis, which can blind. Once the patient is stable, the isolate is susceptible and follow-up cultures are negative, step down to oral fluconazole 400 to 800 mg daily. In neutropenia, prefer an echinocandin or liposomal amphotericin B 3 mg/kg daily, stepping down to fluconazole as neutrophils recover. [7]

Treat Candida auris as a healthcare pathogen, not a yeast. Isolate the patient, notify infection control and public health, identify the species with MALDI-TOF or molecular methods, and treat by susceptibility — many isolates resist multiple classes and need amphotericin B, echinocandins or combination therapy with infectious-diseases input.[10][11]

[7] [9]

Definitive therapy — the stepwise ladder

The ladder moves from topical to oral to intravenous as disease deepens, and every rung is paired with correcting the cause. Topical nystatin or azoles for cutaneous disease; oral fluconazole or itraconazole for extensive, recurrent or mucosal disease; echinocandins for invasive disease.[1][2]

Cutaneous candidiasis

First-line is topical nystatin or a topical azole (clotrimazole 1 percent, miconazole 2 percent, econazole 1 percent, ketoconazole 2 percent) applied twice daily for two to four weeks. The non-drug half of the prescription is what prevents relapse: dry and de-occlude the folds — keep them clean and dry, use a cool hair dryer, apply absorbent or antifungal powder, lose weight, control diabetes and incontinence. Napkin dermatitis adds frequent changes, airing and a barrier cream (zinc oxide or petrolatum) plus a topical azole or nystatin when satellites are present. [1][13]

Oral candidiasis and angular cheilitis

Mild thrush responds to nystatin suspension 100,000 units per mL, 4 to 6 mL swished and swallowed four times daily for 7 to 14 days, or clotrimazole troches 10 mg dissolved in the mouth five times daily; miconazole oral gel is a useful alternative. Moderate, severe, immunosuppressed or recurrent disease prefers oral fluconazole 100 to 200 mg daily for 7 to 14 days. Angular cheilitis gets a topical antifungal to the commissures plus denture, nutritional and moisture control, with a brief mild topical steroid only for inflammation. [3][16]

Vulvovaginal candidiasis and balanitis

Uncomplicated VVC is a single oral fluconazole 150 mg or a topical azole cream or pessary for one to seven days. In pregnancy, use topical azoles only — oral fluconazole is avoided, especially in the first trimester. Severe or recurrent VVC — classically four or more episodes in twelve months — may need fluconazole 150 mg every 72 hours for three doses, then suppressive fluconazole 100 to 200 mg weekly for six months after culture confirmation and diabetes exclusion. Recurrent balanitis should prompt diabetes and HIV testing, and symptomatic partners are treated to break the ping-pong cycle. [4][6][7]

Chronic candidal paronychia

Four pillars: protect the hands from wet work with cotton-lined rubber gloves, emollients and barrier creams; apply a topical antifungal (clotrimazole, miconazole or ciclopirox) to the nail fold for four to eight weeks; add a topical anti-inflammatory if dermatitis dominates; and for refractory disease give oral itraconazole 200 mg twice daily for one week per month over two to three months or fluconazole 150 mg weekly. Surgical marsupialisation is a last resort. [14]

Chronic mucocutaneous candidiasis

CMC needs long-term systemic azoles — fluconazole or itraconazole first-line, posaconazole for refractory or azole-resistant disease — while the immune defect is investigated by immunology with STAT1, STAT3, AIRE and IL-17-pathway genetics. In STAT1 gain-of-function disease, the JAK1/2 inhibitor ruxolitinib can restore IL-17 responses and induce remission, and associated endocrine failure (hypoparathyroidism, adrenal insufficiency, hypothyroidism) must be screened for and treated. [8][15][17][18][19][20]

[1] [7]

Oesophageal candidiasis — the AIDS-defining illness

Odynophagia and dysphagia in HIV or immunosuppression is oesophageal candidiasis until proven otherwise — and topical therapy cannot reach it. Treat empirically with systemic fluconazole 200 to 400 mg daily for 14 to 21 days, especially when the CD4 count is under 200. Reserve endoscopy for refractory or atypical cases, or when CMV or HSV co-infection is suspected. [7]

Candida auris — colonisation, outbreaks and the infection-control machine

C. auris colonises skin — especially axilla and groin — and persists for months, seeding outbreaks in long-term care and ICU. Infection presents as fever, sepsis, wound infection, otitis or pneumonia; multidrug resistance is the rule, so treatment follows susceptibility. Contact precautions, environmental cleaning and public-health notification are not optional, and decolonisation is not yet reliable.[10][11]

How candidiasis patients come to harm — the preventable list

• Candidemia in a febrile neutropenic patient given oral fluconazole alone instead of an echinocandin and line removal — the preventable death.[7][9]
• Treating intertrigo with a topical steroid alone, which flattens the inflammation and worsens the infection.[1]
• Oral fluconazole in pregnancy, especially the first trimester, when a topical azole was the safe choice.[6]
• Misdiagnosing chronic paronychia as acute bacterial and incising a fold that needed dry-work measures.[14]
• Failing to investigate CMC for endocrine autoimmunity or a STAT1 defect, so a treatable immune disease stays hidden.[8][15]
• Leaving an infected central line in place and so perpetuating candidemia.[7]
• Relying on topical therapy for oesophageal candidiasis, where the drug never reaches the mucosa.[7]

Prognosis and disposition

Uncomplicated cutaneous and mucosal candidiasis has an excellent prognosis when the predisposing factor is controlled, and most patients are managed in primary care. Recurrent vulvovaginal candidiasis relapses often after suppression stops — warn the patient. Chronic paronychia recurs in 30 to 50 percent if wet work resumes before the cuticle regenerates. CMC needs lifelong management and endocrine surveillance. Invasive candidiasis and Candida auris carry significant mortality — candidemia around 20 to 40 percent even with treatment — highest in ICU and persistent neutropenia.[5][9]

Patients going home need clear instructions: continue topical therapy for 7 to 14 days, or one week past clearance; follow up if not improving in one to two weeks; and return for HIV and diabetes testing if the disease is recurrent or atypical. Refer to dermatology for atypical or refractory rashes, to infectious diseases for invasive or C. auris disease, and to immunology for suspected CMC.[1][6]

Special populations

[1] [10]

Evidence, guidelines and regional differences

The IDSA 2016 candidiasis guideline is the landmark for invasive disease — echinocandin first-line for candidemia, line removal, ophthalmology review, fluconazole step-down. The AWMF 2021 VVC guideline defines uncomplicated versus complicated disease and recommends culture for recurrent cases; the Taudorf 2019 review anchors the cutaneous evidence base.[1][6][7]

The mantra, and the mnemonic

[1] [1]

The mantra: find the moisture, fix the sugar, scrape the fold — and reach for the echinocandin the moment the patient turns septic.[1][7]

Ward-round test — three stems, thirty seconds each

Stem 1 — the diabetic woman from the top of the topic (answer)

A 54-year-old with type 2 diabetes has her fourth episode in a year of bright-red, moist, satellite-pustuled intertrigo under the breasts and in the groin. What is the diagnosis, the bedside test, and why does it keep relapsing? Model: Candidal intertrigo in poorly controlled diabetes. Confirm at the bedside with KOH microscopy showing budding yeasts and pseudohyphae (and note the satellite pustules, absent in tinea and inverse psoriasis). It relapses because two causes are uncorrected — hyperglycaemia crippling neutrophils, and moisture and occlusion in deep folds. Treat with a topical azole twice daily for two to four weeks and optimise glucose, dry the folds with a cool hair dryer, apply absorbent powder, and counsel on weight and loose cotton clothing. Add oral fluconazole only if disease is extensive or fails topical therapy.[1][13]

Stem 2 — the febrile neutropenic patient with a line (answer)

A 38-year-old with acute leukaemia, day 9 of induction, has a central line and persistent fever despite broad-spectrum antibiotics. Blood cultures grow Candida. What is the first drug, and what two non-drug steps must accompany it? Model: This is candidemia in a febrile neutropenic patient. Start an intravenous echinocandin (caspofungin 70 mg load then 50 mg daily, micafungin 100 mg daily, or anidulafungin 200 mg load then 100 mg daily) per IDSA 2016. The two non-drug steps are removal of the infected central line (source control) and ophthalmology review to exclude endophthalmitis. Step down to oral fluconazole once the patient is stable, the isolate is susceptible, and follow-up cultures are negative.[7][9]

Stem 3 — the patient with lifelong candidiasis (answer)

A 16-year-old has had persistent oral, nail and skin candidiasis since infancy despite repeated courses of topical therapy, and recently developed hypocalcaemia. What is the likely diagnosis, the genetic culprit to test, and an advanced therapy that targets it? Model: Chronic mucocutaneous candidiasis — the lifelong, mucocutaneous-restricted pattern plus endocrine autoimmunity (here hypoparathyroidism with hypocalcaemia) points to an immune defect, classically APECED (AIRE) or a STAT1 gain-of-function mutation suppressing the IL-17 axis. Confirm with immunology and genetic testing, treat with long-term systemic azoles (fluconazole or itraconazole, posaconazole if resistant), screen and replace the endocrine failures, and — in STAT1 gain-of-function disease — consider the JAK1/2 inhibitor ruxolitinib, which restores IL-17 responses and can induce remission.[8][15][18]

References

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19. [19]Mössner R, Diering N, Bader O, et al. Ruxolitinib Induces Interleukin 17 and Ameliorates Chronic Mucocutaneous Candidiasis Caused by STAT1 Gain-of-Function Mutation Clin Infect Dis, 2016.PMID 26787170
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