Urinary Tract Infection - Introduction

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Types of UTIs. UTIs are generally classified as:

• Uncomplicated or complicated, depending on the factors that trigger the infections
• Primary or recurrent, depending on whether the infection is occurring for the first time or is a repeat event

Uncomplicated Urinary Tract Infections (UTIs)

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.

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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.

Click the icon to see an image of the kidney.

Complicated Urinary Tract Infections

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:

• Some anatomical or structural abnormality that impairs the ability of the urinary tract to clear out urine and therefore bacteria.
• Catheter use in the hospital setting or chronic indwelling catheter in the outpatient setting,
• Bladder and kidney dysfunction, or kidney transplant (especially in the first 3 months after transplant).

Recurrences occur in up to 50 - 60% of patients with complicated UTI if the underlying structural or anatomical abnormalities are not corrected.

Recurrent Urinary Tract Infections

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: