An in-depth report on the causes, diagnosis, treatment, and prevention of urinary tract infections.
A urinary tract infection (UTI) is a condition where one or more parts of the urinary system (the kidneys, ureters, bladder, and urethra) become infected. UTIs are the most common of all bacterial infections and can occur at any time in the life of an individual. Almost 95% of cases of UTIs are caused by bacteria that typically multiply at the opening of the urethra and travel up to the bladder. Much less often, bacteria spread to the kidney from the bloodstream.
The Urinary System. The urinary system helps maintain proper water and salt balance throughout the body and also expels urine from the body. It is made up of the following organs and structures:
Defense Systems Against Bacteria. Infection does not always occur when bacteria are introduced into the bladder. A number of defense systems protect the urinary tract against infection-causing bacteria:
Types of UTIs. UTIs are generally classified as:
Uncomplicated UTIs are due to a bacterial infection, most often E. coli. They affect women much more often than men.
Cystitis. Cystitis, or bladder infection, is the most common urinary tract infection. It occurs in the lower urinary tract (the bladder and urethra) and nearly always in women. In most cases, the infection is brief and acute and only the surface of the bladder is infected. Deeper layers of the bladder may be harmed if the infection becomes persistent, or chronic, or if the urinary tract is structurally abnormal.
Pyelonephritis (Kidney Infection). Sometimes the infection spreads to the upper tract (the ureters and kidneys). This is called pyelonephritis, or more commonly, a kidney infection.
Complicated infections, which occur in men and women of any age, are also caused by bacteria but they tend to be more severe, more difficult to treat, and recurrent. They are often the result of:
Recurrences occur in up to 50 - 60% of patients with complicated UTI if the underlying structural or anatomical abnormalities are not corrected.
Most women who have had an uncomplicated UTI have occasional recurrences. About 25 - 50% of these women can expect another infection within a year of the previous one. Between 3 - 5% of women have ongoing, recurrent urinary tract infections, which follow the resolution of a previous treated or untreated episode.
Recurrence is often categorized as either reinfection or relapse:
When a person has no symptoms of infection but significant numbers of bacteria have colonized the urinary tract, the condition is called asymptomatic UTI (also called asymptomatic bacteriuria). The condition is harmless in most people and rarely persists, although it does increase the risk for developing symptomatic UTIs.
Screening for asymptomatic bacteriuria is not necessary during most routine medical examinations, with the following exceptions:
Azzarone G, Liewehr S, O'Connor K. Cystitis. Pediatr Rev. 2007 Dec;28(12):474-6.
Colgan R, Nicolle LE, McGlone A, Hooton TM. Asymptomatic bacteriuria in adults. Am Fam Physician. 2006 Sep 15;74(6):985-90.
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.
Mori R, Lakhanpaul M, Verrier-Jones K. Diagnosis and management of urinary tract infection in children: summary of NICE guidance. BMJ. 2007 Aug 25;335(7616):395-7.
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.
UMMC is a member of the University of Maryland Medical System,
22 S. Greene Street, Baltimore, MD 21201. TDD: 1-800-735-2258 or 1.866.408.6885