Although organisms such as enterococci or group B streptococci are often detected along with Escherichia coli in cultures of voided midstream urine, they usually are not found in cultures of catheter urine, according to a study of premenopausal women published in the the New England Journal of Medicine (2013;369:1883-1891).

Thomas M. Hooton, MD, of the University of Miami, and colleagues analyzed 202 paired specimens of midstream urine and catheter urine from 226 women, aged 18 to 49 years, who had symptoms of cystitis, to assess the predictive values for detection of enterococcus and group B streptococci in midstream urine.

The researchers found that even low levels of E. coli had a high positive predictive value (93% at 10² colony-forming units per milliliter) for bladder bacteriuria. In contrast, though found in cultures of midstream urine, enterococci (10% of cultures) and group B streptococci (12% of cultures) did not predict bladder bacteriuria at any colony count.

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“Cultures of voided midstream urine in healthy premenopausal women with acute uncomplicated cystitis accurately showed evidence of bladder E. coli but not of enterococci or group B streptococci, which are often isolated with E. coli but appear to rarely cause cystitis by themselves,” the investigators wrote.