Asymptomatic Bacteriuria (ASB) Protocol
Antimicrobial and screening framework for adult pregnant patients in primary care.
1. Initial Screening & Urinalysis Filter
Triggered following routine urine albumin/sugar testing if urine albumin is positive.
Nitrite Positive (+ve)
- Action: Send a specimen for formal urine culture & sensitivity (C&S).
- Prescribing Note: May consider initiating immediate empiric antibiotics if the patient is near term or falls into a high-risk group.
Nitrite Negative (-ve)
AND Leukocyte Positive (+ve)
- Action: Send a specimen for formal urine culture & sensitivity (C&S).
- Await the formal lab culture results before initiating targeted antimicrobial treatment.
Nitrite Negative (-ve)
AND Leukocyte Negative (-ve)
- Diagnostic Rule: Asymptomatic Bacteriuria cannot be entirely ruled out by a negative dipstick.
- Action: Send a urine C&S if the patient belongs to a high-risk group AND exhibits persistent proteinuria ≥ x2.
Patients presenting with Diabetes Mellitus, structural or functional renal tract abnormalities, past or recent renal calculi, or a documented history of recurrent urinary tract infections.
2. Urine Culture (C&S) Result Interpretation
Review formal quantitative lab colony counts to isolate true bacteriuria from environmental contamination.
🟢 CFU ≥ 10⁵ total total total
OR ≥ 10⁴ for Group B Streptococcus (GBS)
Confirmed Asymptomatic Bacteriuria:
- Action: Start targeted outpatient antibiotic treatment immediately.
- Follow-up: A repeat check or test-of-cure urine C&S is NOT routinely required following course completion.
🟡 CFU 10³ – 10⁴ OR < 10³
CFU 10³ – 10⁴: Results are borderline or equivocal. A **repeat urine C&S** is officially recommended to clarify diagnosis.
CFU < 10³: Negative culture sequence. No infection isolated. **End of workflow**; withhold antimicrobials.
💊 Recommended Obstetric Antimicrobial Dosage
Empirical and targeted choices for adult pregnant outpatients. Standard course duration is 5 days for all selections.
| Antibiotic Option | Dosing Regimen | Duration | Obstetric Remarks & Safety Cautions |
|---|---|---|---|
| Nitrofurantoin |
50 – 100mg PO q6h (Immediate Release) OR 100mg PO q12h (Modified Release) |
5 Days |
Preferred Choice • Reasonable to offer in the first trimester if no other alternatives are available. • Contraindicated if eGFR < 30 ml/min and MUST be avoided in the third trimester. |
| Cephalexin | 1g – 2g / day PO administered in 2 – 4 divided doses | 5 Days |
Preferred Choice Safe, first-line structural beta-lactam utility across all gestational stages. |
| Amoxicillin / Clavulanate | 625mg PO q8h | 5 Days |
Alternative Choice • Generally safe in pregnancy (FDA Category B). • Warning: Associated with an increased incidence of Necrotizing Enterocolitis (NEC) in preterm neonates and infants born after Premature Rupture of Membranes (PROM). |
| Ampicillin / Sulbactam | 375mg – 750mg PO q12h | 5 Days | Alternative Choice |
| Cefuroxime | 500mg PO q12h | 5 Days | Alternative Choice |