3. Back or abdominal pain
This symptom is more frequent in upper urinary tract infections. This pain is due to the inflammation and distention of the urethra, bladder, ureters, and the capsule that covers and protects the kidneys.
Patients usually refer to pain in the flank or lumbar fossa on the most affected side, but they can experience pain in the lower abdomen too (usually women).
4. Involuntary relaxation of the bladder sphincter
This symptom is specially noticed in bigger children and adults, who can return to wetting their beds during the night. Sphincter relaxation is produced by the irritation of these muscles by bacteria.