Concept of Significant Bacteriuria


Concept of Significant Bacteriuria

Significant Bacteriuria therapy Bacteriuria does not necessarily indicate that the patient has pyelonephritis or cystitis. Rather, it is an important and generally reliable laboratory finding that indicates an abnormal situation, reflecting either the presence of or potential for, infection of the urinary tract. It is an excellent guide to early diagnosis and evaluation of therapy because signs and symptoms of infection may be absent or disappear without a bacteriologic cure, The normal urinary tract is free of bacteria except near the external urethral meatus. In both sexes, some organisms are normally present in the distal urethra.

These are usually similar to the flora of the skin and frequently consist of staphylococci and diphtheroids. Urine is a variable culture medium, depending upon pH, tonicity, and its constituents. High concentrations of urea, low pH, hyperosmolality, and products of dietary organic acids are generally unfavorable to bacteria. In addition, the dynamics of urine flow, or washout, and antibacterial properties of the lining membrane of the urinary tract appear to be important defense mechanisms. The large bowel is considered to be the reservoir of most of the bacteria that invade the urinary tract because of the high frequency of aerobic coliforms found in urinary tract infections.

Several possible pathways from the lumen of the intestine to the urinary passages and kidneys can be postulated. There has been some dispute regarding their relative importance. The principal possibilities are the hematogenous, the lymphatic, and the “ascending” routes. The “ascending” pathway, involving the migration of bacteria from the anus to the periurethral zone and through the urethra to the bladder, is the most favored at the present time. This route can be demonstrated experimentally, particularly in the presence of obstruction or a covering, tt bosky. It also fits in well with the very much higher rate of urinary infections in the female, whose urethra is shorter than that of the male, and with the marked frequency of urinary infections associated with instrumentation of the urethra and bladder.

Clear instances of the hematogenous origin of urinary infection have been demonstrated, particularly in the presence of staphylococcal or gram-negative bacteremia, but these are relatively less common. Clinical Manifestations. The manifestations of pyelonephritis are discussed elsewhere (see Pyelonephritis). Symptoms of cystitis and urethritis include frequency of urination, burning pain on urination, and passage of cloudy, occasionally blood-tinged urine. The patient may complain of a foul odor to the urine, lassitude, and suprapubic discomfort. Fever and leukocytosis are rarely evident in urinary tract infection confined to the bladder and urethra; as a general rule, their presence should be looked upon as evidence of infection of the upper part of the tract. Nevertheless, the absence of fever and leukocytosis does not by any -erns exclude the possibility of kidney involves Course.

The symptoms of inflammation of the lower urinary tract tend to disappear after several days even without a bacteriologic cure. Recurrence of symptomatic infection is frequent in this group. Bacteriuria also tends to be highly recurrent. In the unobstructed patient, this is usually associated with reinfection with a new bacterial strain. Early recurrence, however, is frequently due to the emergence of bacteria from a partially suppressed focus. Persistent infection with the same organisms should alert the physician to the presence of obstruction, calculus, or neurogenic lesions. Frequent follow-up examination of the patient's urine is essential to the management to be described below.

Concept of Significant Bacteriuria. Bacteriuria literally means the presence of bacteria in the urine. The concept of “significant bacteriuria” was introduced to distinguish between bacteria that are actually multiplying in the urine from contaminants in collection vessels, periurethral tissues, the urethra itself, and gross fecal or vaginal contamination. This separation can be accomplished by knowledge of the site and manner in which the urine is collected from the patient and enumeration of the number of organisms present in the sample. The criterion of 100,000 or more organisms per milliliter of urine for diagnosis of significant bacteriuria is an excellent operational definition when the clean voided method is used to collect specimens. It is based on the finding that contaminants will usually be present at numbers ranging from 1000 to 10,000 per milliliter.

Organ-isms found in urinary tract infections grow well in urine; they usually achieve concentrations greater than 100,000 and are often in the range of 1 to 10 million per milliliter. With proper instruction and cleansing, and prompt processing or refrigeration of specimens, it is usually not difficult to obtain reliable results by the clean voided method in both males and females. It is emphasized that, because the reliability of the method will differ with experience and care, it is often wise to avoid overdiagnosis by obtaining multiple specimens, particularly in asymptomatic patients. Thus, survey and screening procedures for bacteriuria generally require _ two or three consecutive positive specimens, indicating that the patient has “persistent significant bacteriuria.”

Bacterial counts lower than 100,000 per milli-liter may occur in patients with true bacteriuria, but when the clean voided method is used, these counts can only be established as valid when shown to be persistent and when the same species of bacteria and preferably the same serotype can be repeatedly isolated. Bacterial counts are higher when urine is allowed to incubate for some time in the bladder. A first-morning specimen is preferred but is not essential. Low or borderline counts may be due to dilution in a well-hydrated patient. Aseptic methods of collection of urine such as from the renal pelvis or ureter, or by bladder puncture, permit the diagnosis of significant bac-


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