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A 4-year retrospective study, in adult patients, of the prognostic value of semi-quantitative bacteruria counts in the diagnosis of group B streptococcus urinary tract infection, "Beyond the Abstract," by Kimberly B. Ulett, MD

BERKELEY, CA (UroToday.com) - Urinary tract infections (UTIs) are among the most common infectious diseases of humans, with up to 40% of healthy adult women experiencing at least one UTI episode in their lifetime.[1] Diagnosis of UTI in adults is based on a combination of symptoms and laboratory findings, including semi-quantitative bacteruria counts (s-QBC). The threshold of ‘significance’ for interpreting s-QBC based on clean catch specimens was historically > 105 cfu/mL.[2, 3, 4, 5] However, recognition of the importance of the clinical scenario has resulted in lower thresholds of >103 cfu/mL, and >104 cfu/mL for different clinical scenarios and different causal organisms.[6, 7] Such lower thresholds improve the sensitivity of detection without undue practicality, although these have not yet translated widely into clinical practice, as noted elsewhere.[8, 9, 10]

In this study, which used clinical and laboratory data of 1 593 patients with Streptococcus agalactiae, also known as Group B Streptococcus (GBS), the authors showed that s-QBC as a prognostic marker are not useful in distinguishing between acute UTI vs asymptomatic bacteriuria (ABU) in adult patients.[11] Data collected over a 4-year period showed that low-count s-QBC was often associated with acute infection, and therefore should not be regarded as transient flora or contaminants in the presence of symptoms indicative of UTI. These findings are consistent with the studies cited above as well as other recent papers highlighting the value of lower s-QBC cut-offs in the setting of adult patients infected with other uropathogenic bacteria.[4, 12, 13] In this study, the authors also showed that older age (age > 40) was similarly predictive of acute UTI compared to s-QBC for GBS specifically, which is of interest given the limitations of a applying and interpreting s-QBC cut-offs for diagnosis of acute UTI in adult patients.

The important take-home point from this study is that GBS, like several other bacterial uropathogens, can cause acute UTI at low s-QBC values. Thus, low s-QBC values for this organism should not always be considered a contaminant or non-pathological in the setting of symptoms and other urinalysis findings that are consistent with acute UTI. The traditionally accepted 105 CFU/ml cut-off value for acute UTI is insensitive for GBS. In the case of GBS UTI, clinical judgement remains important for the diagnosis of UTI.

References:

  1. Foxman, B. 2002. Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. Am. J. Med. 113 Suppl 1A:5S-13S.
  2. Kass, E. H. 1957. Bacteriuria and the diagnosis of infections of the urinary tract; with observations on the use of methionine as a urinary antiseptic. A.M.A. Archives of Internal Medicine 100:709-714.
  3. Savage, W. E., S. N. Hajj, and E. H. Kass. 1967. Demographic and prognostic characteristics of bacteriuria in pregnancy. Medicine (Baltimore) 46:385-407.
  4. Rubin, R. H., E. D. Shapiro, V. T. Andriole, R. J. Davis, and W. E. Stamm. 1992. Evaluation of new anti-infective drugs for the treatment of urinary tract infection. Infectious Diseases Society of America and the Food and Drug Administration. Clin. Infect. Dis. 15 Suppl 1:S216-227.
  5. Colgan, R., L. E. Nicolle, A. McGlone, and T. M. Hooton. 2006. Asymptomatic bacteriuria in adults. Am. Fam. Physician 74:985-990.
  6. Le, J., G. G. Briggs, A. McKeown, and G. Bustillo. 2004. Urinary tract infections during pregnancy. Ann. Pharmacother. 38:1692-1701.
  7. Wilson, M. L., and L. Gaido. 2004. Laboratory diagnosis of urinary tract infections in adult patients. Clin. Infect. Dis. 38:1150-1158.
  8. Walsh, C. A., and K. H. Moore. 2011. Overactive bladder in women: does low-count bacteriuria matter? A review. Neurourol. Urodyn. 30:32-37.
  9. Patterson, T. F., and V. T. Andriole. 1997. Detection, significance, and therapy of bacteriuria in pregnancy. Update in the managed health care era. Infect. Dis. Clin. North Am. 11:593-608.
  10. Kunin, C. M., L. V. White, and T. H. Hua. 1993. A reassessment of the importance of "low-count" bacteriuria in young women with acute urinary symptoms. Ann. Intern. Med. 119:454-460.
  11. Tan, C. K., K. B. Ulett, M. Steele, W. H. Benjamin, Jr., and G. C. Ulett. 2012. Prognostic value of semi-quantitative bacteruria counts in the diagnosis of group B streptococcus urinary tract infection: a 4-year retrospective study in adult patients. BMC Infect. Dis. 12:273.
  12. Nicolle, L. E. 2008. Uncomplicated urinary tract infection in adults including uncomplicated pyelonephritis. Urol. Clin. North Am. 35:1-12, v.
  13. Burd, E. M., and K. Sue Kehl. 2011. A Critical Appraisal of the Role of the Clinical Microbiology Laboratory in the Diagnosis of Urinary Tract Infections. J. Clin. Microbiol. 49:S34-S38.

 

Written by:
Kimberly B. Ulett, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

Department of Infectious Diseases, Royal Brisbane and Women’s Hospital, Herston, Queensland, Australia 4026

Prognostic value of semi-quantitative bacteruria counts in the diagnosis of group B streptococcus urinary tract infection: A 4-year retrospective study in adult patients - Abstract