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

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