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.

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

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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.