Candidiasis (Thrush)

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What is Candidiasis?

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Candidiasis, also known as thrush, is an infection caused by a group of microscopic fungi or yeast infection. These fungi live on our body surface normally but can become infective if your immune system is reduced (immunodeficiency) or if changes occur in the skin's normal bugs. Candidiasis is the most common fungal infection in humans.

Candida can affect virtually any organ throughout the body including:

Mucous membranes - The lining of the oral cavity and pharynx (oral thrush) and vagina are common sites of infection.
Internal organs - Including the meninges (membranes surrounding the brain and spinal cord), kidney and endocardium (inner lining of the heart muscle).
Widespread dissemination (spread of infection) occurs in severely immunosuppressed patients (such as those with HIV).

There are about 20 species of Candida, however the most common species that causes infection is Candida albicans. All the other subtypes can cause similar syndromes to Candida albicans.

Who gets Candidiasis?

Candidiasis is the commonest cause of fungal infection in people with reduced body's immune system. However it can occur in healthy adults too. Approximately 75% of Australian women will experience at least one episode of Candida of the vagina/vulva (outer section of the female genitalia) during their lifetime. Nearly half of all women have been affected by the time they reach 25 years.

In HIV positive individuals who are not receiving therapy over 90% will have oropharyngeal candidiasis (thrush) while 10% will have at least one episode of oesophageal candidiasis.

While immunocompromised patients will have higher risk of candidiasis, oropharyngeal candidiasis is found in 30-55% of healthy young adults. Between 20-50% of healthy women are also said to carry the fungus in the genital tract.

Predisposing Factors

The human body normally has many different types of bacteria and fungi throughout different areas, called the normal flora. There is normally a balance between healthy bugs. A number of physiological conditions can disrupt the normal balance of the flora and lead to overgrowth of specific bugs, such as Candida. Hormonal changes associated with menopause or pregnancy therefore are associated with as increased risk of candida infection in the vagina area. In addition, use of certain oral contraceptive pills (with large amounts of oestrogen) can predispose to the development of thrush in this area.

As for the more severe form of candidiasis, patients with reduced immune system are at risk.

The following conditions predispose a person to reduced immunity:

Blood related cancers such as leukaemias. This is because this disrupts the normal blood counts, including white blood cells that normally fight infection.
Recipients of organ or blood stem cell transplants.
Chemotherapy for different diseases.

Other risk factors for candidiasis:

Extremes of age - Neonates (0-3months) often get candida around the anal area (nappy rash) and oral thrush. In adults, oral and gastrointestinal candidiasis become more common with age.
Diabetes mellitus.
Long term high dose steroid use.
Strong antibiotic use.
Central venous catheters.
Patients on total parenteral nutrition (this means on food supplied though the vessels due to difficulty eating by the patient).
Renal failure needing dialysis.
Surgical procedures in the abdomen.

Progression

Depending on the site of infection, candidiasis is generally relatively benign (not serious). Given time, some may resolve spontaneously when the normal microorganisms start to return to the areas affected by candidiasis (restoring the normal balance of flora). Generally localised candidiasis such as the skin or vagina responds well to antifungal medications.

However in patients with reduced immune function, candidiasis may run on a more serious course. Infection can be long-standing with 'on and off' episodes. In severely immunocompromised individuals, the infection can become resistant to antifungal therapy. Severe oral and oesophageal thrush can lead to a vicious cycle of poor oral intake, malnutrition, generalised wasting, and early death. If Candida enters the blood stream it can spread to and infect other areas such as the bone, meninges, heart and lungs. Widespread infections of candidiasis are serious and can lead to severe generalised infection and death. The mortality rate of a systemic infection (spread throughout the entire body and bloodstream) may be higher than 70% depending on the underlying cause for the infection.

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