Urinary Tract Infection Diagnosis and Treatment

Laboratory Diagnosis

• Laboratories should report Group B Streptococcus (GBS) in urine culture specimens when present at concentrations of ≥10⁴ colony-forming units/ml in pure culture or mixed with a second microorganism, as per CDC guidelines 1
• Proper specimen collection is crucial to minimize contamination 1

Screening and Treatment

• The USPSTF strongly recommends screening all pregnant women for asymptomatic bacteriuria and treating with antibiotics if positive, with urine culture being the gold standard for detection 2, 3, 4, 5
• Asymptomatic bacteriuria is defined as the presence of bacteria in the urine of a person without symptoms of a urinary tract infection, with specific criteria for women (≥10⁵ UFC/mL of the same microorganism in two consecutive urine samples), men (≥10⁵ UFC/mL of a bacterial species in a clean-catch urine sample), and catheterized patients (≥10² UFC/mL of a bacterial species in a urine sample) 4
• The American College of Obstetricians and Gynecologists and the Infectious Diseases Society of America recommend screening all pregnant women for asymptomatic bacteriuria at least once in early pregnancy, optimally at 12-16 weeks gestation 3, 4, 5
• Antimicrobial therapy for 4-7 days is preferred over shorter duration, with first-line options including nitrofurantoin 100mg BID, cephalexin 500mg QID, and ampicillin 500mg QID (if susceptible), as recommended by the American College of Obstetricians and Gynecologists 5, 6
• Fluoroquinolones, tetracyclines, and trimethoprim-sulfamethoxazole should be avoided in the first and third trimesters 5
• Treatment reduces the risk of pyelonephritis from 20-35% to 1-4% in pregnant women, and decreases the risk of low birth weight and preterm delivery, with significant reductions in pyelonephritis rates demonstrated in healthcare centers 5, 4
• Implementation of screening and treatment programs for ASB in pregnant women has demonstrated significant reductions in pyelonephritis rates, from 1.8% to 0.6% and from 2.1% to 0.5% in different healthcare centers, as stated by the American College of Obstetricians and Gynecologists and the Centers for Disease Control and Prevention 4

Special Populations

• Patients with catheters should have a urine culture obtained before the procedure, and antimicrobial therapy should be initiated shortly before the procedure, but not continued after the procedure unless a permanent catheter remains in place, as recommended by the Infectious Diseases Society of America 6, 4
• The treatment of asymptomatic bacteriuria in other populations, such as women who are not pregnant, patients with diabetes, and older adults, is not recommended unless specific criteria are met, due to the risk of antimicrobial resistance 6, 5, 4, 7

Follow-up and Recurrence

• Periodic screening for recurrent bacteriuria should be undertaken following therapy, and follow-up urine culture should be obtained 1-2 weeks after completing therapy to ensure clearance of bacteriuria, as recommended by the American College of Obstetricians and Gynecologists 4, 5
• If bacteriuria persists, retreatment with a different antibiotic based on susceptibility is recommended 5
• There is insufficient evidence to recommend for or against repeat screening during pregnancy following an initial negative culture or after treatment of an initial episode of ASB 5

Complications and Hospitalization

• If pyuria progresses to pyelonephritis, hospitalization and parenteral antibiotics are typically required, with initial IV antimicrobial options including fluoroquinolones, aminoglycosides (with/without ampicillin), or extended-spectrum cephalosporins 8
• Prompt imaging to rule out obstruction or stone disease is essential 8