What is the source of thrush infections in adults, and what is the best course of treatment and prevention of future outbreaks? I have gargled with nystatin and received relief, but with a second occurrence of the problem nystatin produced little relief.

Howard

Thrush is an oral infection due to Candida, a common yeast. It causes painless, white, curd-like plaques (patches) on the tongue and other mucous-membrane surfaces in the mouth. Scraping removes these plaques, leaving a bleeding, painful surface.

Thrush is frequently diagnosed incorrectly. Other non-infectious abnormalities of the tongue can be confused with thrush. These include harmless conditions called "geographic tongue" and "hairy tongue." A physician can make a definitive diagnosis by scraping away part of the plaque and examining it under a microscope. Culturing the material (growing it in the laboratory) is not conclusive, since most healthy people have some Candida in their mouths, which will grow when cultured.

Thrush can occur in normal, healthy individuals, but it is much more common in people receiving certain medications or with certain medical conditions. For example, antibiotics prescribed to treat a bacterial infection can also kill off the normal bacteria in the mouth, allowing the resident yeast to overgrow. (Vaginal yeast infections often occur for this same reason.) Similarly, medications that alter the immune system commonly cause oral thrush. Inhaled corticosteroid therapy given for asthma and oral or intravenous (IV) steroids given for a variety of conditions are among the most frequent offenders.

Malignancies and other conditions that alter immunity may also be at fault. Infection with HIV (human immunodeficiency virus, which causes AIDS) often causes yeast infections in the mouth, the esophagus and other mucous-membrane surfaces. While the chance of your having HIV is not very high, I usually give an HIV test to all patients who have thrush without any other obvious predisposition to it.

The treatment of thrush is rather simple. Topical therapy with nystatin (Mycostatin) or clotrimazole (Mycelex) is usually effective. This can be with liquid preparations or with "troches," substances that dissolve in the mouth like candy. In some circumstances, systemic (whole-body) therapy is necessary.

You state that you did not benefit from your second trial of nystatin therapy. This could be because the Candida in your mouth is resistant to this medication. If that is the case, it should still respond to clotrimazole or one of the systemic treatments. The other possibility is that you do not actually have thrush. You should ask your doctor to confirm the diagnosis as I described above. If you indeed have thrush, an evaluation for an underlying cause is probably in order.