A kidney infection commonly occurs when bacteria infects the bladder or urinary tract. The bacteria E. Coli lives in the bowel where they do not cause any harm. However, if the bacteria spreads from the posterior part of your urethra during sex or after using the toilet, you may end up having a kidney infection. Kidney infections are usually accompanied by several symptoms including loss of appetite, groin pain, lower back, stomach upset, and blood in your urine. Every part of the urinary system is sensitive to bacteria and germs. Therefore, a little exposure can result in severe infection.