Bacterial contamination rates for non-clean-catch and clean-catch midstream urine collections in uncircumcised boys

Dr. Saez-Llorens is currently a Pediatric Infectious Disease Fellow at the University of Texas Southwestern Medical Center at Dallas. Submitted for publication June 7, 1988; accepted July 28, 1988. Reprint requests: Jacob A. Lohr. MD. Box 386. The Children's Medical Center of the University ofVirginia. Charlottesville, VA 22908.

CCU     Clean-catch urine
CFU     Colony-forming units

Standard practice for collecting a midstream urine specimen from boys for bacterial culture has included cleansing of the urethral meatus to decrease urine specimen contamination.^1,2 A recently published study³ demonstrated that meatal cleansing did not decrease specimen contamination rates and that contamination rates after collection without cleansing were acceptably low. However, the study did not provide data on the impact of circumcision status, because only 4% (4/102) of the subjects were uncircumcised. Our study was performed to determine whether meatal cleansing affects the rate of bacterial contamination of mid-stream urine specimens collected from healthy, uncircumcised malechildren.

METHODS

Ninety-nine healthy boys, aged 2 to 15 years, were studied. Fifty percent were older than 8 years of age. All the boys were uncircumcised and toilet trained, had no history of renal disease or urinary tract infections, had no congenital or acquired meatal abnormality, had received no antibiotics during the previous week, and were afebrile during the study. The urine specimens were obtained in the pediatric clinic of the Hospital Nacional de Ninos. San Jose, Costa Rica. This site was chosen because most Costa Rican boys are not circumcised. Written informed consent was obtained.

The first urine specimen was obtained at midstream without meatal cleansing and was designated a non-clean-catch urine specimen. From 24 to 30 hours after the first specimen collection. a second midstream specimen was collected after meatal cleansing with 2% castile soap and water; it was designated a clean-catch urine specimen. Meatal cleansing and specimen collection were preceded by a nonforceful attempt to retract the foreskin. When the foreskin was not retracted, direct cleansing of the meatus could not take place. All specimens were collected in sterile wide-mouth containers, under the supervision of a nurse, and were processed immediately in an on-site microbiology laboratory. The urine specimens were cultured according to standard microbiologic methods. The culture media used were trypticase soy agar with 5% sheep blood and MacConkey agar¹. The culture plates were inoculated with the use of a 0.01 ml calibrated loop. Routine procedures wereused for species identification.

A sterile urine culture was defined as one producing no growth. A contaminated culture was defined as one growing a single organism with fewer than 10⁴ colony-forming units per milliliter of urine, or two or more organisms. A positive culture was defined as one growing one organism with 10⁸ CFU/ml urine.

RESULTS

Non-CCU specimens and CCU specimens were obtained from 99 uncircumcised boys. Cultures of 90 (91%) of the non-CCUs and of 94(95%) of the CCUs were sterile. Cultures of seven (7%.) of the non-CCUs were contaminated and cultures of two (2%) were positive. Cultures of three (3%) of the CCUs were contaminated, and cultures of two (2%) were positive. One of the contaminated non-CCU cultures and one of the contaminated CCU cultures were from the same patient. In addition, one of the positive non-CCU cultures and one of the positive CCU cultures were from the same patient, but the two cultures did not grow the same organism.

Twenty-four isolates were identified during the study; 17 were gram-negative organisms and seven were staphylococci. The 10 contaminated non-CCU and CCU cultures collectively yielded Escerichia coli, Proteus mirabilis, Klebsiella sp., Pseudomonas aeruginosa. Staphylococcus aureus, and coagulase-negative staphylococci. Of these contaminated cultures, two grew one organism, six grew two organisms, and two grew three organisms. The organisms that accounted for the four positive urine cultures were S. aureus, Serratia liquefaciens, Morganella margagnii, and P. aeruginosa. All subjects with a positive urine culture underwent urine collection for a repeat culture, and all of the repeat cultures were sterile.

The difference in the sum of the contamination rate and the positive rate between the uncleansed and the cleansed boys (9% vs 5%) was not statistically significant (Fisher exact test; p = 0.2). Moreover, given the study size and the observed rates of contamination (positivity) in the compared groups, it is unlikely that the true difference in these rates was as large as 10% (5% vs 15%; p = 0.05).

DISCUSSION

An epidemiologic study published more than 25 years ago noted bacterial contamination in only 15 (0.9%) of 1647 urine specimens collected from school-aged boys (circumcision status of the boys was not noted) without specific preparation before voiding.⁴ Despite this evidence, a current recommendation by the author of that study¹ and by others² includes meatal cleansing of males before collection of a voided urine specimenfor culture.

A recent study³ of urine contamination rates included 102 healthy boys, 98 of whom were circumcised. In these circumcised boys, 5% of non-CCU cultures were contaminated and 10% of 85 CCU cultures were contaminated (9%) or positive (1%) These differences in contamination and positive rates were not statistically significant. The authors concluded that cleansing of the urethral meatus prior to collecting a urine specimen for culture from circumcised boys has no demonstrable benefit.³

When the results from this study of uncircumcised boys were compared with those from the previously studied circumcised boys, there were no apparent differences. The contamination rate was 3% to 9%, and the positive rate was 0% to 2% regardless of circumcision status or prior cleansing. Follow-up study of the subjects with positive urine cultures in the previous study and in the present study showed sterile urinary cultures without intervening treatment, so these patients were probably not infected when the original positive culture was obtained. Thus the positive cultures were probably contaminated cultures.

The organisms isolated in our study of uncircumcised boys were gram-negative species in most cases. In contrast, the organisms isolated in the previous study³ of circumcised boys were corynebacteria, streptococci, and staphylococci. The importance of this interesting difference is not clear.

We conclude that even in uncircumcised males, meatal cleansing does not significantly decrease rates of contaminated urine cultures or positive urine cultures; that rates of contaminated and positive urine cultures after no cleansing are acceptably low; and that rates of contaminated and positive urine cultures do not appear to differ from ratesof cultures of urine from circumcised boys.

We thank Gregory Hayden, MD, for his review and advice.

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