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Urinary tract infection - Causes

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of urinary tract infections.

Alternative Names

Cystitis; UTI

Causes:

The bacterial strains that cause UTIs include:

Escherichia (E.) coli is responsible for most uncomplicated cystitis cases in women, especially in younger women. E. coli is generally a harmless microorganism originating in the intestines. If it spreads to the vaginal opening, it may invade and colonize the bladder, causing an infection. The spread of E. coli to the vaginal opening most commonly occurs when women or girls wipe themselves from back to front after urinating, or after sexual activity.
Staphylococcus saprophyticus accounts for 5 - 15% of UTIs, mostly in younger women.
Klebsiella, Enterococci bacteria, and Proteus mirabilis account for most of remaining bacterial organisms that cause UTIs. They are generally found in UTIs in older women.
Rare bacterial causes of UTIs include ureaplasma urealyticum and Mycoplasma hominis, which are generally harmless organisms.

Organisms in Severe or Complicated Infections

The bacteria that cause kidney infections (pyelonephritis) are generally the same bacteria that cause cystitis. There is some evidence, however, the E. coli strains in pyelonephritis are more virulent (able to spread and cause illness).
Complicated UTIs that are related to physical or structural conditions are apt to be caused by a wider range of organism. E. coli is still the most common organism, but others include Klebsiella, P. mirabilis, and Citrobacter.
Fungal organisms, such as Candida species. (Candida albicanscauses the "yeast infections" that also occur in the mouth, digestive tract, and vagina.)
Other bacteria associated with complicated or severe infection include Pseudomonas aeruginosa, Enterobacter, and Serratia species, gram-positive organisms (including Enterococcus species), and S. saprophyticus.

Bacterial Strains in Recurrent UTIs

Recurring infections are often caused by different bacteria than those that caused a previous or first infection.

Factors in Overcoming the Bacterial Defense Systems

Changes in the amount or type of acid within the genital and urinary tracts are contributors to lowering the resistance to infection. For example, beneficial organisms called lactobacilli increase the acidic environment in the female urinary tract. Reductions in their number (which, for example, occurs with estrogen loss after menopause), increase pH and therefore the risk of infection.

Resources

http://kidney.niddk.nih.gov -- National Kidney and Urologic Diseases Clearinghouse
www.urologyhealth.org -- American Urological Association
www.acog.org -- American College of Obstetricians and Gynecologists

References

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Conway PH, Cnaan A, Zaoutis T, Henry BV, Grundmeier RW, Keren R. Recurrent urinary tract infections in children: risk factors and association with prophylactic antimicrobials. JAMA. 2007 Jul 11;298(2):179-86

Faust WC, Pohl HG. Role of prophylaxis in vesicoureteral reflux. Curr Opin Urol. 2007 Jul;17(4):252-6.

Foster RT Sr. Uncomplicated urinary tract infections in women. Obstet Gynecol Clin North Am. 2008 Jun;35(2):235-48, viii.

Hodson EM, Wheeler DM, Vimalchandra D, Smith GH, Craig JC. Interventions for primary vesicoureteric reflux. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD001532.

Jepson RG, Craig JC. Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev. 2008 Jan 23;(1):CD001321.

Lin K, Fajardo K; U.S. Preventive Services Task Force. Screening for asymptomatic bacteriuria in adults: evidence for the U.S. Preventive Services Task Force reaffirmation recommendation statement. Ann Intern Med. 2008 Jul 1;149(1):W20-4.

Litwin MS, Saigal CS, editors. Urologic Diseases in America. US Department of Health and Human Services, Public Health Service, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases. Washington, DC: US Government Printing Office, 2007; NIH Publication No. 07-5512.

Modgil G, Baverstock A. Should bubble baths be avoided in children with urinary tract infections? Arch Dis Child. 2006 Oct;91(10):863-5.

Moore KN, Fader M, Getliffe K. Long-term bladder management by intermittent catheterisation in adults and children. Cochrane Database Syst Rev. 2007 Oct 17;(4):CD006008.

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Norrby SR. Approach to the patient with urinary tract infection. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap.306.

Perrotta C, Aznar M, Mejia R, Albert X, Ng CW. Oestrogens for preventing recurrent urinary tract infection in postmenopausal women. Cochrane Database Syst Rev. 2008 Apr 16;(2):CD005131.

Peterson J, Kaul S, Khashab M, Fisher AC, Kahn JB. A double-blind, randomized comparison of levofloxacin 750 mg once-daily for five days with ciprofloxacin 400/500 mg twice-daily for 10 days for the treatment of complicated urinary tract infections and acute pyelonephritis. Urology. 2008 Jan;71(1):17-22.

Pohl A. Modes of administration of antibiotics for symptomatic severe urinary tract infections. Cochrane Database Syst Rev. 2007 Oct 17;(4):CD003237.

Roussey-Kesler G, Gadjos V, Idres N, Horen B, Ichay L, Leclair MD, et al. Antibiotic prophylaxis for the prevention of recurrent urinary tract infection in children with low grade vesicoureteral reflux: results from a prospective randomized study. J Urol. 2008 Feb;179(2):674-9; discussion 679. Epub 2007 Dec 20.

Shaikh N, Morone NE, Lopez J, Chianese J, Sangvai S, D'Amico F, Hoberman A, Wald ER. Does this child have a urinary tract infection? JAMA. 2007 Dec 26;298(24):2895-904.

U.S. Preventive Services Task Force. Screening for asymptomatic bacteriuria in adults: U.S. Preventive Services Task Force reaffirmation recommendation statement. Ann Intern Med. 2008 Jul 1;149(1):43-7. Ann Intern Med. 2008 Jul 1;149(1):W20-4.

Williams GJ, Wei L, Lee A, Craig JC. Long-term antibiotics for preventing recurrent urinary tract infection in children. Cochrane Database Syst Rev. 2006 Jul 19;3:CD001534.

Reviewed last on: 8/4/2009
Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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