Significance of bacteriuria with presumed non-pathogenic organisms

The results of 2,793 clean catch midstream specimens submitted to the microbiology laboratory were examined to determine if the isolation of reputed non-pathogens such as Lactobacillus, Staphylococcus epidermidis. Micrococcus and diphtheroids represented poor collection technique, contaminant growth by failure to plate or refrigerate quickly or actual urinary tract infection. Eight per cent of the inpatient cultures and 18 per cent of the outpatient cultures had more than 10(5) colony-forming units per ml. of these non-pathogens. Of the outpatient cultures with more than 10(5) colony-forming units per ml. of non-pathogens 44 per cent had symptoms of urinary tract infection and more than 10 white blood cells per high power field in the urinary sediment, compared to 3 per cent of inpatients. In a prospective analysis of an outpatient population a second clean catch midstream specimen was collected within 2 hours of the first specimen with careful attention to sterile collection technique. Of 15 cases of significant bacteriuria with non-pathogens in the first specimen only 1 had significant bacteriuria with the same organism in the second specimen. In contrast, in the inpatient population 7 of 11 cases with pathogen significant bacteriuria in the first specimen had significant bacteriuria in the second specimen. These findings suggest that most episodes involving isolation of non-pathogens in greater than 10(5) colony-forming units per ml. from urine represent poor techniques of specimen collection rather than urinary tract infection.