Candidiasis (Thrush, Yeast Infection)

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.

Statistics on 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.

Risk Factors for Candidiasis

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 of Candidiasis

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.

Symptoms of Candidiasis

Candidiasis can present with a range of different symptoms depending on which area of the body is affected. You should see your doctor if you notice any of the following symptoms:

Oral candidiasis - This may produce discomfort in the mouth (often described as 'cottony feeling'), loss of taste, pain on eating and swallowing.
Oesophageal - Pain on swallowing, focal pain in behind the breast bone area.
Vulvovaginal - Itching (pruritis), whitish/cottage-cheese discharge, vaginal irritation, pain during intercourse, pain on urination, and increased menstrual cramping may be present.
Urinary tract - Painful urination, increased frequency.
Ocular - Painful eye, gradual decrease in vision.
Bone and joints - Slowly progressive pain and decreased joint movement.
Meninges - fever, neck stiffness, altered mental status, headache.
Heart - Fever, symptoms of heart failure such as ankle swelling and shortness of breath.
Liver and spleen - Swinging persistent fever, pain on right upper side of the abdomen, nausea, vomiting and loss of appetite.
Gastrointestinal - Constipation, diarrhoea or mucus in the stool.
Lungs - Fever, shortness of breath.
Acute disseminated candidiasis - Symptoms range from mild fever to a severe inflammatory response syndrome.

When you present to your doctor they will ask detailed questions about your symptoms and duration. They will also ask several questions about your general medical history and sexual history to determine if you have any predisposing factors.

Clinical Examination of Candidiasis

The clinical signs of candidiasis vary depending on which area of your body is infected. The following outlines some of the major signs of Candida infection. Your doctor will carefully examine the area involved to determine whether it has the typical appearance of Candida.

Oral thrush - Typically you may notice a white coating or plaque on the surface of the tongue or other areas within the mouth. Sometimes Candida can grow under dentures so appropriate hygiene is essential.
Vulvovaginitis - Infection of the vulva and vagina can cause redness and itching in the genital area. Your doctor will perform a speculum examination to look at the inner walls of the vagina and to detect any discharge (which is usually 'cottage cheese-like' in character.
Eye - Infection at the back of the eye can be seen as white areas using an ophthalmoscope.
Acute widespread candidiasis - If Candida enters the bloodstream it tends to cause fever but in some cases can lead to a full-blown sepsis syndrome including low blood pressure, cool and clammy skin and confusion.

How is Candidiasis Diagnosed?

Often the diagnosis of Candida can be made clinically if superficial infection is present. However you may need to have a number of tests to help confirm the diagnosis. These may include:

Routine blood tests including a full blood count, liver function tests (LFT) and renal function tests. These can give an indication whether infection is present, whether organs such as the liver are involved and give a baseline level of your organ function to guide treatment.
Blood culture - Samples of blood will be collected so that the yeast can be grown in the laboratories. Unfortunately not all cases of systemic infection will have positive blood cultures so the diagnosis can sometimes be difficult.
Swabs and scrapings - Small samples of tissues from the skin, mouth, or vagina are obtained and examined under the microscope. This helps to determine whether fungi/ yeast are present which have classic features such as budding hyphae (branching segments). In suspected vulvovaginal candidiasis swabs are obtained using a speculum (similar to a pap smear). The pH level of the vagina is tested and then the smear examined for fungi.
Other cultures - Depending on the suspected site of infection, your doctor may order samples of your sputum, joints, urine or cerebrospinal fluid. Again these can be examined carefully to see if any fungi is present.
Imaging - Sometimes a chest x-ray or CT scan of the abdomen may help confirm the site of infection. Upper gastrointestinal endoscopy is useful for the diagnosis of oesophageal candidiasis.

Prognosis of Candidiasis

Prognosis of candidiasis varies widely depending on the site of disease. In superficial candidiasis affecting the skin or mucosal surface (such as the oral cavity and vagina), the prognosis is very good and almost all will respond to antifungal medications. However in patients with low immune system, candidiasis may lead to premature death due to malnutrition and generalised wasting (as described above).

How is Candidiasis Treated?

Treatment of Candida infections depends on the severity of the disease and the site of involvement. Usually antifungal agents can clear the infection.

Superficial infections of the skin or genitals are generally fairly easily treated. The latter can be treated with local creams or vaginal pessaries (tablets inserted into the vagina) or oral tablets (which may be more convenient and preferred by patients). Sometimes your doctor may recommend a combination of these treatments. Likewise if your oesophagus is involved you may be treated with tablets (fluconazole) or oral solutions (itraconazole).

If you have a widespread infection it is important that you are treated in hospital. This not only allows treatment of the actual infection but allows investigations for possible causes of damage to the immune system. You may be screened for HIV infection, diabetes mellitus or leukaemia if you have recurrent or severe infections.

Severe Candida infections may threaten the function of organs. You may need to be seen by specialists (such as lung doctors, gastrointestinal doctors, neurologists or eye doctors) for more definitive treatment. Occasionally surgery may be necessary to remove infected tissues. In widespread candidiasis, stronger antifungal agents such as amphotericin B or caspofungin may also be needed.

If you have recurrent episodes of Candida infections your doctor may recommend you take a regular low-dose of anti-fungal mediations. This is called prophylactic therapy and basically reduces the risk of re-infection. However there is debate as to whether this is effective as it can sometimes lead to resistant infections.

Candidiasis References

Bennett J. 'Candidiasis' (Chpater 187) in Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison's Principles of Internal Medicine. 16th Edition. McGraw-Hill. 2005.
Denning D, Fortnightly Review: Management of genital candidiasis, BMJ 1995; 310: 1241-1244.
DoctorFungus: Invasive Candidiasis Overview, 2005. Available [online] from: URL: http://www.doctorfungus.org/Mycoses/human/candida/InvasiveOverview.htm
Henderson S, Magana R. Candidiasis, eMedicine, 2006. Available [online] from URL: http://www.emedicine.com/emerg/topic76.htm
Kumar, Clark. Clinical Medicine, 5th Edition, Saunders, 2002.
Longmore, Wilkinson, Rajagopalan. Oxford Handbook of Clinical Medicine, 6th Edition, Oxford University Press, 2004.