How should I manage a 23‑week pregnant woman with asymptomatic bacteriuria caused by Enterococcus faecalis at 10,000–49,000 CFU/mL?

Treatment of Asymptomatic Bacteriuria in Pregnancy at 23 Weeks

You should treat this patient with a 4–7 day course of targeted antibiotics based on susceptibility testing, because pregnant women with untreated asymptomatic bacteriuria face a 20–35% risk of developing pyelonephritis (reduced to 1–4% with treatment) and increased risks of preterm delivery and low birth weight. 1, 2

Why Treatment is Mandatory in Pregnancy

• Pregnancy is one of only two populations (along with patients undergoing urologic procedures with mucosal trauma) where screening for and treating asymptomatic bacteriuria is strongly recommended by the Infectious Diseases Society of America (Grade A-I recommendation). 1, 3

• Untreated asymptomatic bacteriuria increases the risk of preterm birth from approximately 53 per 1,000 to 14 per 1,000 when treated, and reduces very low birth weight risk from 137 per 1,000 to 88 per 1,000. 2

• The American College of Obstetricians and Gynecologists considers screening and treatment of asymptomatic bacteriuria a standard of care in pregnancy. 2

Colony Count Interpretation

• Your patient's colony count of 10,000–49,000 CFU/mL meets the diagnostic threshold for asymptomatic bacteriuria in pregnancy. 1, 4

• For pregnant women, a single voided specimen with ≥10^5 CFU/mL defines bacteriuria, but the IDSA guidelines note that the traditional 100,000 CFU/mL threshold was based on morning collections in adults, and that 10,000–100,000 CFU/mL represents a transition range where infection is clinically significant. 1

• Any urine specimen with ≥10^4 CFU/mL of group B Streptococcus is significant in pregnancy, and similar lower thresholds apply when clinical context supports infection. 4

• In your case with Enterococcus faecalis at 10,000–49,000 CFU/mL in an asymptomatic pregnant woman at 23 weeks, treatment is indicated because the consequences of untreated bacteriuria in pregnancy outweigh any uncertainty about colony count. 1, 2

Recommended Antibiotic Regimen

• Duration: Treat for 4–7 days (the IDSA recommends 3–7 days, but most contemporary evidence supports 4–7 days for optimal microbiological cure). 1, 2, 5

• Agent selection: Base your choice on the susceptibility pattern of the isolated Enterococcus faecalis. 1

• First-line options for Enterococcus faecalis (if susceptible):

  • Ampicillin or amoxicillin are typically effective against Enterococcus faecalis and are safe in pregnancy. 6
  • Nitrofurantoin is often preferred for urinary tract infections in pregnancy due to its safety profile and effectiveness, though Enterococcus species may show variable susceptibility. 5, 7
  • Avoid single-dose regimens, as they show lower bacteriuria clearance rates compared to short-course therapy. 2

• Seven-day regimens provide better microbiological cure rates than one-day regimens, though clinical outcomes may be similar; in the context of pregnancy, prioritize the longer course to maximize eradication. 5

Post-Treatment Follow-Up

• Obtain a follow-up urine culture after completing antibiotics to confirm clearance of bacteriuria. 2

• Continue periodic screening with urine cultures throughout the remainder of pregnancy, because recurrence is common (occurring in a substantial proportion of treated women) and each recurrence requires re-treatment. 1, 2

• The IDSA explicitly recommends periodic screening for recurrent bacteriuria following therapy (Grade A-III recommendation). 2

Common Pitfalls to Avoid

• Do not withhold treatment based on the absence of symptoms—asymptomatic bacteriuria in pregnancy is a distinct clinical entity that requires treatment regardless of symptom status. 1, 3

• Do not be reassured by the absence of pyuria—pyuria accompanying asymptomatic bacteriuria is not required for diagnosis or treatment decisions in pregnancy. 1, 8

• Do not assume a single negative culture later in pregnancy means the patient is protected—continue screening throughout pregnancy after any treated episode. 2

• Do not use colony count alone to dismiss the culture—while 10,000–49,000 CFU/mL is below the traditional 100,000 threshold, the clinical context of pregnancy and the specific organism (Enterococcus faecalis, a known uropathogen) warrant treatment. 1, 4

Why This Differs from Non-Pregnant Populations

• In premenopausal non-pregnant women, diabetic women, elderly patients, and catheterized patients, treatment of asymptomatic bacteriuria is not recommended (Grade A-I) because it does not reduce symptomatic infections, mortality, or morbidity, and increases adverse drug events and antimicrobial resistance. 1, 3

• Pregnancy fundamentally changes the risk-benefit calculation because untreated bacteriuria progresses to pyelonephritis in 20–35% of cases and causes measurable harm to both mother and fetus. 2