A fecal Gram Stain should be done at least annually during your bird's health check. The good news is that yeast can easily be treated in most cases. Anything that increases the acidity in the digestive tract will control a mild yeast infection. Dr. Greg Harrison recommends adding a teaspoon of Organic, non pasteurized, non-filtered, organic Apple Cider Vinegar to a pint of their drinking water. I use a Probiotic in my birds drinking water about three times a week.
Probiotics contain lactobacillus that helps promote good bacteria to grow in their digestive tract.
When yeast infections become more difficult to treat, your Avian Veterinarian can prescribe a number of antifungals such as Nystatin, Kectoconazoal or Fluconazole. When it is read it is important to observe that the yeast are budding or reproducing. Some food products or supplements may contain Brewers yeast. These will appear in the Gram Stain, but this yeast is not alive and doesn't cause problems in the bird, therefore, it should not be treated as a yeast infection. Yeast that have been affected by antifungal treatments will appear as hollow blue shells.