Urinary Tract Infection - Introduction

Classifications Based on Symptoms and Levels of Infection. UTIs can also occur without symptoms and with symptoms but very low bacterial levels.

When bacteria are present and there are no symptoms it is called asymptomatic UTI or also bacteriuria.
Some patients can also have symptoms of infection with very low bacterial counts. In such cases, the condition is called acute urethral syndrome.

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Uncomplicated Urinary Tract Infections (UTIs)

Cystitis. Cystitis is the most common urinary tract infection and is sometimes referred to as acute uncomplicated UTI. 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). When infection spreads to the upper tract (the ureters and kidneys) it is called pyelonephritis, or more commonly, kidney infection. As many as half of all women with cystitis may have infections of the upper urinary tract at the same time as cystitis.

Click the icon to see an image of the kidney.

Urethritis. When infection is limited only to the urethra, the infection is known as urethritis. This is a common sexually transmitted disease in men.

Complicated Urinary Tract Infections

Complicated UTIs may develop because of any one of a number of physical problems and affect any gender and age group. The common feature in most complicated UTIs is the inability of the urinary tract to clear out bacteria because of a physical condition that causes obstruction to the flow of urine or problems that hinder treatment success.

Recurrent Urinary Tract Infections

Most women who have had an uncomplicated UTI have occasional recurrences. A quarter to a half of these women can expect another infection within a year of the previous one. Between 3% of 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:

Reinfection. About 80% of recurring UTIs are reinfections. A reinfection occurs several weeks after antibiotic treatment has cleared up the initial episode and can be caused by the same bacterial strain that caused the original episode or a different one. The infecting agent is usually introduced through the rectal region from fecal matter and moves up through the urinary tract.
Relapse. Relapse is the less common form of recurrent urinary tract infection. It is diagnosed when a UTI recurs within two weeks of treatment of the first episode and is due to treatment failure. Relapse usually occurs in kidney infection (pyelonephritis) or is associated with obstructions such as kidney stones, structural abnormalities, or, in men, chronic prostatitis.