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Are Urine Cultures in Nonpregnant Women with Uncomplicated Cystitis Useful?

Summary and Comment |
November 13, 2013

Are Urine Cultures in Nonpregnant Women with Uncomplicated Cystitis Useful?

  1. Anna Wald, MD

Paired midstream and catheter urine cultures correlated well if E. coli was the uropathogen, but poorly if gram-positive organisms were found.

  1. Anna Wald, MD

Although cystitis is one of the most common infections in young women, interpretation of urine cultures remains uncertain. Investigators conducted a study involving 202 nonpregnant women (median age, 22) with symptoms of cystitis in whom paired urine cultures — one from clean-catch midstream urine and the other from urine obtained with bladder catheterization — were assayed.

Escherichia coli, the most common pathogen, was found in both samples from 120 women; even counts as low as 102 colony-forming units in midstream urine were strongly associated with bacterial isolation from catheter urine. In contrast, for enterococci and group B streptococci, colony counts in midstream urine were not predictive of bacterial isolation from the bladder; in more than half of cases (61%), E. coli was also isolated from catheter urine.

Comment

These findings in nonpregnant women confirm that Escherichia coli is the most common cause of cystitis, and suggest that even low levels of E. coli in midstream urine cultures (i.e., 102 colony-forming units) can indicate bladder infection. However, gram-positive organisms in such cultures are rarely indicative of uncomplicated cystitis, even if they are isolated concurrently with E. coli. Hence, we can continue to provide empiric, short-course antibiotics for uncomplicated cystitis without obtaining midstream cultures — and if cultures are obtained, the laboratory should report any growth of E. coli at ≥100 colonies per mL of urine.

  • Disclosures for Anna Wald, MD at time of publication Consultant / Advisory board AiCuris; Amgen Royalties UpToDate Grant / research support Agenus; Genentech; Genocea; Gilead; NIH; NIH-NCI; NIH-NIAID; NIH-NIGMS

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