Hello and welcome to Just Answer. I am a licensed veterinarian and would be happy to answer your questions.
There are various reasons for a dog to lose hair and bacterial infections are just one of them. Other reasons can include mange mites, ringworm (fungal infections), hormonal imbalances or allergic dermatitis. What is most concerning is that the hair did not grow back after the problem was treated. This would seem to indicate that the treatment was not effective and/or perhaps it wasn't treating the correct problem.
I would recommend that you have him re-evaluated by your veterinarian soon and make sure they are aware that the hair did not grow back. They may want to check his thyroid or check him for a condition called Cushings disease. Also they may want to better evaluate his skin and rule out the above mentioned conditions.
In the meantime, an antiseptic shampoo from the pet store can decrease the bacteria and yeast if they are present. I like the product called Hexedene® because it contains chlorhexidine which is effective on bacteria and yeast.
I hope that helps. Please let me know if you have any further questions.
Applying the steroid may help short term, but the cause of the hair loss needs to be identified before a more long-lasting treatment can be recommended. Shampooing may help to decrease any surface of bacteria and yeast, but he really needs to see a vet to diagnose the problem, especially since it either recurred or never resolved.
There is not much more that can be done at home.