Pyelonephritis is a kidney infection. It is usually bacterial in origin and stems from an infection in another part of the urinary tract, such as the bladder. Pyelonephritis can occur in anyone, although it is more likely to occur in women. Symptoms of pyelonephritis include pain or burning during urination, an urgent need to urinate, fever, nausea with or without vomiting, hematuria, and pain, particularly in the sides and groin. Left untreated, pyelonephritis can lead to further kidney infections, scarring, chronic kidney disease, or permanent damage. Serious infections can spread to other parts of the body, including the blood.