Urinary Tract Infection

The two forms of urinary tract infection (UTI) are cystitis (infection of the bladder) and urethritis (infection of the urethra). UTI is nearly 10 times more common in females than in males (except in elderly males) and affects 10% to 20% of all females at least once. UTI is also a prevalent bacterial infection in children, with girls again more commonly affected than boys. In adult males and in children, UTIs are typically associated with anatomic or physiologic abnormalities and therefore need close evaluation. Most UTIs respond readily to treatment, but recurrence and resistant bacterial flare-up during therapy are possible.

Causes

Most UTIs result from ascending infection by a single gram-negative, enteric bacterium, such as Escherichia coli, Klebsiella, Proteus, Enterobacter, Pseudomonas, or Serratia. In a patient with neurogenic bladder, an indwelling urinary catheter, or a fistula between the intestine and bladder, UTI may result from simultaneous infection with multiple pathogens.

Studies suggest that infection results from a breakdown in local defense mechanisms in the bladder that allows bacteria to invade the bladder mucosa and multiply. These bacteria can’t be readily eliminated by normal urination.

The pathogen’s resistance to the prescribed antimicrobial therapy usually causes bacterial flare-up during treatment. Even a small number of bacteria (fewer than 10,000/ml) in a midstream urine specimen collected during treatment casts doubt on the effectiveness of treatment.

In most patients, recurrent UTIs result from re-infection by the same organism or by some new pathogen. In the remaining patients, recurrence reflects persistent infection, usually from renal calculi, chronic bacterial prostatitis, or a structural anomaly that is a source of infection. The high incidence of UTI among females is likely due to the natural anatomic features of females that facilitate infection. (See UTI risk factors.)

Complications

Untreated chronic UTI can seriously damage the urinary tract lining. Infection of adjacent organs and structures (for example, pyelonephritis) may also occur. When this happens, the prognosis is poor.

Assessment Findings

The patient may complain of urinary urgency and frequency, dysuria, bladder cramps or spasms, itching, a feeling of warmth during urination, nocturia, and urethral discharge (in males). Other complaints include low back pain, malaise, nausea, vomiting, pain or tenderness over the bladder, chills, and flank pain. Inflammation of the bladder wall also causes hematuria and fever. The most common initial symptoms of UTI in elderly patients are lethargy and a change in mental status.

Diagnostic Tests

Microscopic urinalysis showing red and white blood cell counts greater than 10 per high-power field suggests UTI. The presence of leukocyte esterase and nitrites may also indicate the presence of bacteria in the urine.
Clean-catch urinalysis revealing a bacterial count of more than 100,000/ml confirms UTI. Lower counts don’t necessarily rule out infection, especially if the patient is urinating frequently, because bacteria require 30 to 45 minutes to reproduce in urine.
Sensitivity testing is used to determine the appropriate antimicrobial drug treatment.
Voiding cystourethrography or excretory urography may disclose congenital anomalies that predispose the patient to recurrent UTI.