Which patients benefit from Asymptomatic Bacteriuria screening?

January 23, 2025 · by · in Health Pathology NSW, Urinary tract infections · Leave a comment

Guest posting Dr Victoria Jordan, Microbiology & Infectious Diseases Registrar, Pathology NSW.

What is asymptomatic bacteriuria (ASB)?

This is the presence of significant bacterial growth ((≥105 colony-forming units [CFU]/mL) in the urine in the absence of urinary symptoms.   It likely occurs via ascension from perineal flora. Commoner with aging:  prevalence 5% in healthy premenopausal women; contrast that with up to 50% of elderly people in care facilities and almost all those who have a long term indwelling urinary catheter.    In general, there is no general evidence that ASB increases the risk of UTI or other adverse effects. Treatment with antibiotics is unnecessary and increases the risk of antibiotic-related side effects, including antimicrobial resistance.

Contamination of midstream urine samples is common and is often difficult to distinguish from ASB.  Contamination occurs from perineal flora (especially enterococci and Group B streptococci), more so in women given the proximity of the perineum to the distal urethra. The absence of squamous cells from the sample does not exclude it.  Most importantly the chance of false positive ASB detection due to contamination increases with suboptimal sample storage – i.e. >2 hours at room temperature) as small quantity of bacteria present will replicate to a detectable amount.

What are the three accepted indications for ASB screening?

  1. Pre-operative urological patients where mucosal trauma during surgery may occur (including biopsy, stent insertion/exchange).  Use 1 dose of targeted antimicrobial within an hour prior to the procedure is sufficient; an entire treatment course is unnecessary.   Note that ASB screening is NOT indicated for any other type of surgery including arthroplasty, vascular and cardiac surgery.
  2. First trimester pregnancy (single screening at 12-16 weeks gestation).  It is recommended to confirm the presence of ASB with a repeat culture to confirm the finding. ASB occurs in 2-7% of pregnant women.   There is an increased risk of UTI including pyelonephritis in this population, especially in those with documented ASB and pyelonephritis has been associated with an increased risk of preterm birth.
  3. Post renal transplant (in the first month only). In the first month after renal transplant, recovery from significant urological surgery is occurring and a urinary catheter and ureteric stent are in situ. Historically, given these risk factors, screening of donor and recipient urine and antibiotic treatment has been usual in this period.  However more recent studies question the clinical utility of ASB screening and treatment even this early post-transplant population, with Antonino et al (2022) finding that treatment did not decrease the incidence of UTI or graft pyelonephritis.  More evidence is required, and several studies are currently in progress in this space.

How should a midstream urine be collected?

  • Use a clean purpose-made container; avoid touching the inside of the container
  • Hold labia or foreskin away from the urethra  – cleansing is NO LONGER recommended
  • Collect the middle part of the stream after passing the first part into the toilet (to ‘flush’ perineal flora away from the distal urethra)
  • Transport the sample to the laboratory within 2 hours or keep refrigerated until transport is available
  • Ensure that the request form states Urine for MCS

 References

  1. Ansaldi Y, Martinez de Tejada Weber B. Urinary tract infections in pregnancy. Clin Microbiol Infect. 2023;29(10):1249-53. doi:10.1016/j.cmi.2022.08.015
  2. Antonio MEE, Cassandra BGC, Emiliano RJD, Guadalupe OLM, Lilian REA, Teresa TGM, et al. Treatment of asymptomatic bacteriuria in the first 2 months after kidney transplant: A controlled clinical trial. Transplant Infectious Disease. 2022;24(6):e13934. doi:https://doi.org/10.1111/tid.13934
  3. Cai T, Mazzoli S, Lanzafame P, Caciagli P, Malossini G, Nesi G, et al. Asymptomatic Bacteriuria in Clinical Urological Practice: Preoperative Control of Bacteriuria and Management of Recurrent UTI. Pathogens. 2016;5(1)doi:10.3390/pathogens5010004
  4. Coussement J, Scemla A, Abramowicz D, Nagler EV, Webster AC. Antibiotics for asymptomatic bacteriuria in kidney transplant recipients. Cochrane Database Syst Rev. 2018;2(2):Cd011357. doi:10.1002/14651858.CD011357.pub2
  5. Honkanen M, Jämsen E, Karppelin M, Huttunen R, Huhtala H, Eskelinen A, et al. The impact of preoperative bacteriuria on the risk of periprosthetic joint infection after primary knee or hip replacement: a retrospective study with a 1-year follow up. Clin Microbiol Infect. 2018;24(4):376-80. doi:10.1016/j.cmi.2017.07.022
  6. Kazemier BM, Koningstein FN, Schneeberger C, Ott A, Bossuyt PM, de Miranda E, et al. Maternal and neonatal consequences of treated and untreated asymptomatic bacteriuria in pregnancy: a prospective cohort study with an embedded randomised controlled trial. Lancet Infect Dis. 2015;15(11):1324-33. doi:10.1016/s1473-3099(15)00070-5
  7. Nicolle LE, Gupta K, Bradley SF, Colgan R, DeMuri GP, Drekonja D, et al. Clinical Practice Guideline for the Management of Asymptomatic Bacteriuria: 2019 Update by the Infectious Diseases Society of America. Clinical Infectious Diseases. 2019;68(10):e83-e110. doi:10.1093/cid/ciy1121
  8. Origüen J, López-Medrano F, Fernández-Ruiz M, Polanco N, Gutiérrez E, González E, et al. Should Asymptomatic Bacteriuria Be Systematically Treated in Kidney Transplant Recipients? Results From a Randomized Controlled Trial. Am J Transplant. 2016;16(10):2943-53. doi:10.1111/ajt.13829
  9. Wiley Z, Jacob JT, Burd EM. Targeting Asymptomatic Bacteriuria in Antimicrobial Stewardship: the Role of the Microbiology Laboratory. J Clin Microbiol. 2020;58(5)doi:10.1128/jcm.00518-18
  10. Wingert A, Pillay J, Sebastianski M, Gates M, Featherstone R, Shave K, et al. Asymptomatic bacteriuria in pregnancy: systematic reviews of screening and treatment effectiveness and patient preferences. BMJ Open. 2019;9(3):e021347. doi:10.1136/bmjopen-2017-021347
  11. Winkler ML, Huang J, Starr J, Hooper DC, Paras ML, Letourneau AR, et al. If you don’t test, they will not treat: Impact of stopping preoperative screening for asymptomatic bacteriuria. Antimicrob Steward Healthc Epidemiol. 2023;3(1):e95. doi:10.1017/ash.2023.166
  12. RANZCOG. Best practice statement: Routine antenatal assessment in the absence of pregnancy complications. (2022). https://ranzcog.edu.au/wp-content/uploads/Routine-Antenatal-Assessment.pdf
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