Most urinary tract infections (UTI) are confined to the bladder and urethra, but some progress through the ureters to the kidneys. Acute pyelonephritis is the term for infection of the upper urinary tract. This condition is more serious than lower UTI, and results in more than 100,000 hospitalizations per year in the United States.
The symptoms of pyelonephritis include fever, chills, flank pain, nausea, and vomiting, in addition to the lower UTI symptoms of frequent urination with pain or burning. Elderly patients may not have fever, and are more likely to have nausea and vomiting. Other conditions with similar symptoms include appendicitis, pelvic inflammatory disease, inflammation of the gall bladder, lower lobe pneumonia. The diagnosis of pyelonephritis is confirmed with a urine culture showing a high concentration of bacteria. The most common type is Escherichia coli. Others include Staphylococcus saprophyticus, Proteus, Klebsiella, and Enterococci. Infection can also spread to the kidneys from other locations through the bloodstream, especially in patients with impaired immune function.
Acute pyelonephritis affects 1 to 2 percent of pregnant women, and increases the risk for premature labor and low birth weight babies. The authors of Reference 1 recommend that all pregnant women with this condition should be hospitalized, for at least a short time, for aggressive hydration and antibiotics. Fluoroquinolone antibiotics should be avoided because of their risk of damage to the fetus, but other antibiotics can be used successfully, including ampicillin, gentamicin, cefazolin, and ceftriaxone.
Antibiotic treatment is usually continued for 7 to 14 days, but may need to be extended to six weeks for some cases. The two most common causes for failure of the initial treatment are (1) infection by antibiotic resistant bacteria, and (2) kidney stones. Other complications include anatomic abnormalities and other infections, such as appendicitis. Short-term antibiotic therapy (3 days) is often used for lower UTI, but this results in a 50% relapse rate for infection that has already spread to the kidneys.