Could my patient with acute dysuria and less than 10,000 E. coli/ml on urine culture still have a urinary tract infection (UTI)?

Absolutely! Although historically ≥100,000 bacteria/ml has been used as a criterion for UTI based on studies of women with pyelonephritis in the 1950s,1 several studies have since found that this criterion may not be met in up to 50% of symptomatic patients with UTI. 2-6 A lower criterion of 100-1,000 bacteria/ml of urine increases the sensitivity of urine culture to ~90% or more for diagnosis of UTI (albeit with lower specificity). 2-5

A 1982 NEJM study involving UTIs due to coliforms in acutely dysuric women found that the traditional count of ≥100,000 bacteria/ml in midstream urine missed ~50% of cases based on positive bladder cultures. 2 Similarly a 2013 NEJM study reported that 40% of women with symptomatic UTI would be missed if the ≥100,000 bacteria/ml criterion for midstream urine is used. 3

Among symptomatic men, 32% have been found to have <100,000 bacteria/ml in their midstream urine 4 and a single urine specimen by urethral catheterization growing ≥ 100 bacteria/ml is consistent with bacteriuria for both men and women. 5

Since most of these studies have involved UTI caused by E. coli or other coliforms, more data are needed to find out if the same findings apply to non-coliform urinary pathogens.

Bonus Pearl: Did you know that because quantitative urine culture results are concentration dependent (ie, “per ml”), a dilute urine—as may be found in patients experiencing diuresis—will result in lower numbers of bacteria/ ml. 5

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 References

  1. Kass EH. Asymptomatic infections of the urinary tract. Trans Assoc Am Physicians 1958;69:56-74. https://pubmed.ncbi.nlm.nih.gov/13380946/
  2. Stamm WE, Counts GW, Running KR, et al. Diagnosis of coliform infection in acutely dysuric women. N Engl J Med 1982;307:463-8. https://pubmed.ncbi.nlm.nih.gov/7099208/
  3. Hooten TM, Roberts PL, Cox ME, et al. Voided midstream urine culture and acute cystitis in premenopausal women. N Engl J Med 2013;369:1883-91. https://www.nejm.org/doi/full/10.1056/NEJMoa1302186
  4. Lipsky BA, Ireton RC, Fihn SD, et al. Diagnosis of bacteriuria in men: specimen collection and culture interpretation. J Infect Dis 1987;155:847-54. https://pubmed.ncbi.nlm.nih.gov/3559288/
  5. Nicolle LE, Bradley S, Colgan R, et al. Infectious Diseases Society of America Guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis 2005;40:643-54. https://pubmed.ncbi.nlm.nih.gov/15714408/
  6. Roberts KB, Wald ER. The diagnosis of UTI: colony count criteria revisited. Pediatrics 2018;141:e20173239. https://doi.org/10.1542/peds.2017-3239

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Could my patient with acute dysuria and less than 10,000 E. coli/ml on urine culture still have a urinary tract infection (UTI)?