Thank you Coaxli Wildcat for your question about powdery mildew.
The short answer is that powdery mildew is usually not a problem for the health of the African Violet until it becomes severe, but it can easily spread to other plants. Isolation of the plant is your first priority if possible.
To prevent powdery mildew, let the top 1/2 inch of the soil dry out before watering again. Too dry is better than too wet.
The soil should be a sharp draining mix with extra sand or perlite.
For infected plants, try to remove infected leaves if possible. This can be challenging with African Violets. Do remove and destroy any dying and dead leaves and destroy them.
TREATMENTS
Brush the mildew with a soft damp tooth brush and clean the brush with alcohol.
2 Sprays to try: 1 tsp baking soda mixed with 1 quart water. 1 tsp vinegar mixed with 1 quart water.
I would first try getting the tooth brush with the baking soda solution and brush the leaves.
Start with one plant or one part of one plant to see how it tolerates the treatment.
Let me know how it goes.