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Glossary · Dysbiosis and disease

Candidiasis

In one sentence

Candidiasis is an infection caused by Candida yeasts, most often Candida albicans. It commonly affects the vulva and vagina or the mouth, and occurs when the yeast overgrows beyond normal colonisation.

Also known as: thrush · vaginal thrush · oral thrush · vulvovaginal candidiasis · vaginal yeast infection

What is candidiasis?

Candida is a yeast that lives harmlessly in the mouth, gut and vagina of many people. Candidiasis is the term for when it overgrows and causes symptoms. Candida albicans is the most common species; others, such as Candida glabrata (now also named Nakaseomyces glabratus), are seen more often in recurrent cases.

The main forms are:

  • Vulvovaginal candidiasis (thrush): itching, soreness, redness and thick white discharge, usually with normal vaginal pH.
  • Oral candidiasis: white plaques on the mucosa, more common in infants, older people with dentures, inhaled corticosteroid users and people who are immunocompromised.
  • Invasive candidiasis: infection of the bloodstream or internal organs in hospitalised or immunocompromised patients; a serious condition quite separate from the mucosal forms.

How it is diagnosed

Vulvovaginal candidiasis is diagnosed from symptoms plus microscopy showing yeasts or pseudohyphae (saline or potassium hydroxide wet mount), or by culture. Under US CDC guidance, it is recurrent when there are three or more symptomatic episodes in less than a year. In recurrence, culture or another species-level test is advised, because non-albicans species can be less susceptible to standard azoles.

The key distinction is colonisation versus infection. Finding Candida without symptoms is common and generally does not need treatment.

Example

A woman has had four episodes of itching and thick discharge in a year, each treated without confirmation. Her gynaecologist takes a swab for culture with species identification, which grows C. glabrata, and this guides the choice of treatment. As a complement, he requests a vaginal microbiota analysis to check for a coexisting bacterial imbalance such as bacterial vaginosis, which also causes discharge and is easily confused with thrush.

Broad-spectrum antibiotics disturb the vaginal microbiota and are associated with more episodes of thrush. Unlike BV, vulvovaginal candidiasis can occur in a community dominated by lactobacilli. The relationship between lactobacilli and Candida is complex, and evidence for probiotics in preventing recurrence is limited.

Candidiasis at Xenogene

Xenogene’s AMC Vaginal profiles the vaginal ecosystem by NGS, fungi included, and according to the product sheet reports Candida species; recurrent vaginal candidiasis is among its listed indications. Candida in a report does not equal infection: interpretation belongs to the healthcare professional who orders the test, alongside symptoms and examination. For oral candidiasis, the oral microbiota test also covers fungi such as Candida.

Frequently asked questions

Is vaginal thrush a sexually transmitted infection?

It is not considered an STI. Candida is part of many people's normal microbiota, and infection usually reflects overgrowth favoured by antibiotics, hormonal changes, poorly controlled diabetes or immunosuppression, among other factors.

When is thrush considered recurrent?

The US CDC defines recurrent vulvovaginal candidiasis as three or more symptomatic episodes in less than a year. In that situation the diagnosis should be confirmed and the species identified, because non-albicans species may respond less well to standard antifungals.

If Candida shows up on a test, do I have thrush?

Not necessarily. Many women carry Candida without symptoms (colonisation), and this is not usually treated. Candidiasis means symptoms plus the yeast. A healthcare professional needs to interpret the finding.

Related terms

  • Vaginal microbiota

    The vaginal microbiota is the community of microorganisms living in the vagina. In many women of reproductive age it is dominated by Lactobacillus species, which produce lactic acid and help keep vaginal pH low.

  • Bacterial vaginosis

    Bacterial vaginosis is a shift in the vaginal microbiota in which lactobacilli decline and anaerobic bacteria such as Gardnerella overgrow. It can cause discharge and odour, but is often symptom-free.

  • Lactobacillus

    Lactobacillus is a genus of Gram-positive, lactic acid-producing bacteria. Species such as L. crispatus, L. gasseri, L. iners and L. jensenii commonly dominate the vaginal microbiota of women of reproductive age.

  • Dysbiosis

    Dysbiosis is a change in the composition or function of the microbiota away from what is considered compatible with health: loss of diversity, loss of beneficial microbes or overgrowth of others.

Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.

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