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Pyelonephritis: When Urinary Tract Infections Reach the Kidneys

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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.

Without proper treatment, pyelonephritis can lead to sepsis, renal abscesses, high blood pressure, and kidney failure. The acute kidney infection causes death in severe cases, with a mortality rate of 7.3 per 1,000 cases in women (16.5 per 1,000 cases in men).


1. Ramakrishnan K et al, “Diagnosis and management of acute pyelonephritis in adults”, American Family Physician 2005 March 1; 71(5): 933-42.

2. Antibiotic Resistant E. Coli Urinary Tract Infections

3. Women, Weight, and Kidney Stones

Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.

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When I was 37 weeks pregnant I woke up in what I considered the worst pain of my life. I remember thinking 'Am I in labor? and if I am I don't EVER want to do this AGAIN!' My husband and step daughter were sleeping. I vomitted ALL of my dinner, the flank pain was unbearable, and I remember just laying in bed in tears. I immediately began drinking bottle after bottle of water and almost immediately realized that I was not in labor but that I had what I like to call "A UTI gone bad". At around 5 am I woke my husband up and told him I was going to the ER. I knew what it was and I knew it was not going away unless I got some antibiotics. As soon as my nurse saw my urine she knew what it was too-- it was so concentrated that it was a brownish/orange color. Sure enough, I had a UTI that had reached my kidneys. The antibiotics were a huge relief by the next night but that kind of pain is something I wouldn't wish upon anyone.

I was in labor with my son one week later and I can't help but feel that this incident had a lot to do with it. Luckily he was healthy and beautiful :)

November 15, 2009 - 6:27pm
Expert HERWriter Guide Blogger

Hi Linda - I read this article with a lot of interest because I had pyelonephritis as a child and was hospitalized for six weeks. At the time I was too young to understand what was going on, just that it was very serious. Thank you for providing such a comprehensive picture.
Take good care,

November 13, 2009 - 6:20pm
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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.