Thrush, also called candidiasis, is a disease caused by a fungus (Candida albicans). Everyone has this fungus both on and inside their bodies. It can be found on the skin, in the stomach, the colon and rectum, the vagina, and in the mouth and throat. Most of the time, Candida albicans is harmless and actually helps keeps bacteria levels in check. Sometimes, however, there is an overgrowth of this fungus, which can lead to a variety of problems.
Both HIV-positive and HIV-negative people can develop candidiasis. Many women experience vaginal yeast infections, a type of candidiasis. Similarly, a person can experience an overgrowth of fungus in their mouth or the back of their throat. Stress, poor diet, or not getting enough rest can contribute to these problems. Also, a person who takes antibiotics for bacterial infections, especially for long periods of time, can develop thrush in their mouth or vagina. Candidiasis in the mouth (oral thrush) can also occur in people who use inhaled steroids, such as those used to treat asthma and other lung problems.
Poor oral hygiene and smoking can also play a role in fungal overgrowth in the mouth. Excessive alcohol and sugar consumption have also been linked to the development of candidiasis.
In HIV-positive people, oral thrush and vaginal yeast infections can occur at any time, regardless of their CD4 cell counts. The more the immune system becomes damaged, oral thrush and vaginal yeast infections are more likely to occur and recur more frequently. HIV-positive people with damaged immune systems, usually with a CD4 cell count less than 200, are also more likely to develop candidiasis deeper in their bodies, such as in their esophagus or their lungs. As with many opportunistic infections, candidiasis will usually improve or recur less often if antiretroviral therapy significantly increases CD4 cell counts.