Acute pyelonephritis, an upper urinary tract infection, describes a clinical syndrome of bacteriuria associated with fever, chills, flank pain or tenderness, and lower urinary tract symptoms (e.g., frequency, urgency, dysuria). Uncomplicated infections are those in healthy, nonpregnant females aged 18–40 years, without underlying comorbidities, structural defects in urinary anatomy, or renal dysfunction. Criteria for complicated infection include extremes of age, male gender, immunosuppression (e.g., diabetes, malignancy), pregnancy, presence of a urinary catheter, an anatomic or functional abnormality, obstruction, or history of instrumentation, or the presence of an unusual or resistant organism.
There are approximately 250,000 cases of acute pyelonephritis annually in the United States, and it is estimated that 30% of these patients are hospitalized. The prevalence of disease is greater in women than men. Men are at higher risk for pyelonephritis if they are uncircumcised, have an enlarged prostate causing urinary stasis, participate in rectal intercourse, or have undergone recent urologic instrumentation or surgery.
Other populations at risk for acute pyelonephritis include those with urinary catheters, spinal cord injury, neurogenic bladder, or fistulae involving the bladder or ureters, or who have undergone renal transplantation. Pregnant women, especially during the second trimester, are also at higher risk for pyelonephritis because of hormonally induced changes in the urinary system. Potential complications of acute pyelonephritis during pregnancy include septicemia, premature labor and low-birth-weight infants.