Urinary tract infection (UTI) is a common infection that usually occurs when bacteria enter the opening of the urethra and multiply in the urinary tract. The urinary tract includes the kidneys, ureters (tubes that carry urine from the kidneys to the bladder), bladder, and urethra (tube that carries urine from the bladder).
The special connection of the ureters at the bladder help prevent urine from backing up into the kidneys, and the flow of urine through the urethra helps to eliminate bacteria. Under normal circumstances, bacteria placed in the bladder are rapidly cleared, partly through the flushing and dilutional effects of voiding but also as a result of the antibacterial properties of urine and the bladder mucosa.
Urinary tract infections usually develop first in the lower urinary tract (urethra, bladder) and, if not treated, progress to the upper urinary tract (ureters, kidneys). Bladder infection (cystitis) is by far the most common UTI. Infection of the urethra is called urethritis. Kidney infection (pyelonephritis) requires urgent treatment and can lead to reduced kidney function and possibly even death in untreated, severe cases.
The causes of urinary tract infection and why some are affected more than others are explained below.
Gender and Sexual activity
The female urethra appears to be particularly prone to colonization with colonic gram-negative bacilli because of its proximity to the anus, its short length (about 4 cm), and its termination beneath the labia. Sexual intercourse causes the introduction of bacteria into the bladder and is temporally associated with the onset of cystitis; it thus appears to be important in the pathogenesis of UTIs in younger women. Voiding after intercourse reduces the risk of cystitis, probably because it promotes the clearance of bacteria introduced during intercourse.
UTIs are detected in 2 to 8% of pregnant women. Upper tract infections, in particular, are unusually common during pregnancy.
Any impediment to the free flow of urine- tumor, stricture, stone, or prostatic hypertrophy-results in greatly increased frequency of UTI. Infection superimposed on urinary tract obstruction may lead to rapid destruction of renal tissue. It is of utmost importance, therefore, when infection is present, to identify and repair obstructive lesions.
Neurogenic Bladder Dysfunction
Interference with the nerve supply to the bladder, as in spinal cord injury, tabes dorsalis, multiple sclerosis, diabetes, and other diseases, may be associated with UTI. The infection may be initiated by the use of catheters for bladder drainage and is favored by the prolonged stasis of urine in the bladder. An additional factor often operative in these cases is bone demineralization due to immobilization, which causes hypercalciuria, calculus formation, and obstructive uropathy.
Defined as reflux of urine from the bladder cavity up into the ureters and sometimes into the renal pelvis, vesicoureteral reflux occurs during voiding or with elevation of pressure in the bladder.
Vesicoureteral reflux is common among children with anatomic abnormalities of the urinary tract as well as among children with anatomically normal but infected urinary tracts. In the latter group, reflux disappears with advancing age and is probably attributable to factors other than UTI. Long-term follow-up of children with UTI who have reflux has established that renal damage correlates with marked reflux, not with infection.
Bacterial Virulence Factors
Bacterial virulence factors markedly influence the likelihood that a given strain, once introduced into the bladder, will cause UTI.
Increasing evidence suggests that host genetic factors influence susceptibility to UTI.
To find out whether you have a UTI, your doctor will test a sample of urine for pus and bacteria. You will collect "midstream" sample of urine in a sterile container. (This method of collecting urine helps prevent bacteria around the genital area from getting into the sample and confusing the test results.)
In the urinalysis test, the urine is examined for white and red blood cells and bacteria. Then the bacteria are grown in a culture and tested against different antibiotics for antibiotic sensitivity, to see which drug best destroys the bacteria.
If you have frequent infections, your doctor may ask you to undertake an ultrasound exam, which gives pictures from the echo patterns of soundwaves bounced back from internal organs.
Or he might ask you to undertake another useful test called cystoscopy. A cystoscope is an instrument made of a hollow tube with several lenses and a light source, which allows the doctor to see inside the bladder from the urethra.