Urinary Tract Infection - Introduction

Highlights	Risk Factors	Medications
Introduction	Complications	Other Treatments
Causes	Diagnosis	Resources
Symptoms	Treatment	References

Introduction

A urinary tract infection (UTI) is a condition where one or more structures in the urinary tract become infected after bacteria overcome its strong natural defenses. In spite of these defenses, UTIs are the most common of all 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 (known as the ascending route). Much less often, bacteria spread to the kidney from the bloodstream.

The male and female urinary tracts are relatively the same except for the length of the urethra.

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Different classifications have been devised to help doctors choose treatments and determine the causes of UTIs.

Primary or Recurrent UTIs. UTIs are classified as primary or recurrent, depending on whether they are the first infection or whether they are repeat events.

Community- or Hospital-Acquired. UTIs are also sometimes grouped according to where they are acquired:

Community-Acquired Infections. Most UTIs are thought to develop in the community at large. It is unclear how primary community-acquired infections occur or how they are spread. Although most cases have been thought to arise sporadically, a rare outbreak caused by drug-resistant bacteria in three states between 1996 and 2000 suggests epidemic spread of community-acquired infections could be more common than previously thought and may be spread via contaminated food. Most community-acquired infections are not serious and probably develop when the intestines become colonized with bacteria that are also predisposed to infecting the urinary tract.
Hospital-Acquired Infections (Nosocomial Infections). UTIs are also commonly acquired in the hospital, often due to contaminated urinary catheters. Hospital-acquired infections (known as nosocomial infections) tend to be more serious because the bacteria that cause them are often resistant to drug treatment and patients are often in poor general health.

Uncomplicated and Complicated. UTIs are also sometimes further defined as either being uncomplicated or complicated depending on the factors that trigger the infections.

Uncomplicated infections are only associated with bacterial infection, most often Escherichia coli (E. coli). They affect women much more often than men.
Complicated infections, which occur nearly as often in men as women, are also caused by bacteria but they occur as a result of some anatomical or structural abnormality. Often they are associated with catheter use in the hospital setting, bladder and kidney dysfunction, or kidney transplant (especially in the first three months after transplant). Recurrences occur in up to 50% to 60% of patients with complicated UTI if the underlying structural or anatomical abnormalities are not corrected.