What can be some possible causes for recurring bacterial infections?

Poor diet: The fuel that you take in is as important for you as it is for your car. Would you risk poor fuel for your car? Stick to "god made" food and leave the "junk" alone. Your immune system requires energy and that comes from oxidation-----the equivalent of burning gas in a car cylinder. Wrong gas, poor engine performance. Empty calories make you sick.

A few: More commonly maybe the initial infection was never killed off properly, maybe, the host environment is conducive for bacterial growth, maybe the bacteria was resistent to the initial treament....Area of the infection is not kept clean.....To name a few.