Kidney infection (pyelonephritis)

Pyelonephritis is an infection in the kidneys and is more serious than a bladder infection (cystitis). Symptoms of a kidney infection include:

• Pain in the back, side, and groin.
• Urgent, frequent urination.
• Pain or burning during urination.
• Fever.
• Nausea and vomiting.
• Pus and blood in the urine.

Like urinary tract infections in general, kidney infections may be either uncomplicated or complicated.

• Uncomplicated kidney infections (acute uncomplicated pyelonephritis) occur in otherwise healthy people who have no conditions that affect kidney and bladder function. They mostly affect younger women.
• Complicated kidney infections (acute complicated pyelonephritis) occur in people who have an impaired immune system or a condition that affects bladder or kidney function. These conditions include diabetes, structural problems within the urinary tract, and obstructions such as kidney stones.

Acute complicated pyelonephritis may lead to:

• Kidney damage from an abscess inside or just outside the kidney.
• Kidney failure.
• A life-threatening infection that spreads into the bloodstream (septicemia). People who are very young or old or who have an impaired immune system have an increased risk of developing this type of infection.

Oral antibiotics usually can treat kidney infections, although brief hospitalization and a short course of intravenous (IV) antibiotics are sometimes required. People tend to be more severely ill with kidney infections than with bladder infections.