Urinary tract infections

Drug Store News, Dec 11, 1989

The most common technique for obtaining urine is the midstream void method. In this method and the three others the patients periurethral area is cleansed with soap. The patient is asked to void and during the mid-point of the stream a portion is collected and sent for culture. It is recommended that if the patient is asymptomatic, midstream samples from two separate voids should be attained. A single specimen is sufficient if a symptomatic patient is being tested. When this method is properly performed and a bacterial count of 105/ml or greater of the same organism is obtained, it is diagnostic of the UTI with a 95 percent detection accuracy.

The whole void method of collection does collect the entire voided specimen. A portion of this is then cultured. A bacterial count of 105/ml or greater of the same organism is diagnostic of the UTI. The accuracy of this method increases as the method is repeated: single void, 80 percent; two separate voids, 91 percent; three separate voids, 95 percent.

The single in and out catheterization method is designed to alleviate the problem of specimen contamination at time of voiding. After cleansing of the periurethral area a catheter is aseptically inserted. The urine is collected and a portion of this sample is cultured. A bacterial count of 105/ml or greater of the same organism is diagnostic with a 95 percent detection accuracy.

The suprapubic aspirate method is performed by inserting a needle in the midline, 2 cm above the symphysis pubis and aspirating the urine. The specimen is then cultured. Because this method goes directly into the bladder a bacterial count of 5x103/ml or greater of the same organism is diagnostic of a UTI. This method has a 99 percent detection accuracy, the highest of the four methods described.

Antibiotic Therapy Principles

The choice of antibiotic for UTI treatment is based on primarily the site of infection, presenting signs and symptoms, whether the infection is complicated or uncomplicated. The side effect potential, drug cost and dosing inconvenience are other considerations in choice. The ideal antibiotic would be well absorbed, tolerated well, achieve high urine concentrations and have a coverage of activity limited to the offending organism. Many of the agents available today are well absorbed and tolerated reasonable well.

The antibiotic should achieve a high urine level because eradication of the UTI is more closely associated with urine rather than serum drug concentration. The kidney has the ability to excrete many antibiotics into the urine in high concentrations, much higher (10 to 100 times) than the simultaneous serum concentration. Some antibiotics that do not achieve high serum levels can be used to effectively treat UTI. Nitrofurantoin, carbenicillin indanyl sodium and sulfonamides are examples.

In the most popular culture and sensitivity test the urine sample is placed on to the culture media and a disc containing the antibiotics used to treat UTI is placed on the plated media. The concentration of antibiotic in the disc is of prime importance because the sensitivity and resistance pattern of the microorganism is based on the size of zone of growth inhibition surrounding a particular antibiotic.