What are the next steps in managing a pregnant female treated with Keflex (Cephalexin) for cystitis if the urine culture is negative?

Management of Pregnant Female with Suspected Cystitis and Negative Urine Culture

Direct Recommendation

If the urine culture is negative in a pregnant woman treated empirically with Keflex for suspected cystitis, stop antibiotics immediately and reassess for alternative diagnoses—do not continue treatment for asymptomatic bacteriuria or culture-negative symptoms. 1

Clinical Approach

Immediate Action When Culture Returns Negative

• Discontinue cephalexin therapy as prescribing antibiotics in the absence of proven bacterial infection provides no benefit and increases antibiotic resistance risk 2
• Do not repeat urine culture if the patient is now asymptomatic, as post-treatment cultures are not indicated when symptoms have resolved 1
• Focus on clinical response rather than laboratory confirmation in asymptomatic patients 1

Key Principle in Pregnancy

The critical distinction here is that pregnancy is the ONE population where screening and treatment of asymptomatic bacteriuria IS indicated 3, but this requires a positive culture showing ≥10^5 CFU/mL 3. A negative culture means:

• No asymptomatic bacteriuria exists to treat
• The initial symptoms were either not from bacterial cystitis or have resolved spontaneously
• Continuing antibiotics is not justified 2

Reassess for Alternative Diagnoses

If symptoms persist despite negative culture, consider:

• Non-infectious causes: Urethral syndrome, interstitial cystitis, pelvic floor dysfunction 4
• Vaginal causes: Vaginitis, which can mimic UTI symptoms—presence of vaginal discharge makes UTI less likely 4, 5
• Low-count bacteriuria: In symptomatic women, even growth as low as 10^2 CFU/mL could reflect true infection 4, though standard culture cutoffs may miss this
• PCR-detectable infection: Research suggests up to 96% of symptomatic women with negative cultures may still have E. coli infection detectable by PCR 6, though this is not clinically actionable in routine practice

When to Obtain Another Culture

Obtain a new urine culture only if: 1

• Symptoms of UTI persist or recur after stopping antibiotics
• Patient develops fever or signs of pyelonephritis
• Before any urological procedure that will breach the mucosa 1, 7

Special Pregnancy Considerations

• Do NOT treat asymptomatic bacteriuria without documented positive culture 3
• Screening culture at 12-16 weeks gestation should have been performed; if this was the screening culture and it's negative, the patient has only 1-2% risk of developing pyelonephritis later in pregnancy 3
• No routine repeat cultures are needed after a negative result unless patient develops febrile illness 1

Common Pitfalls to Avoid

• Do not continue antibiotics "to complete the course" when culture is negative and symptoms resolved—this promotes resistance 1, 2
• Do not treat asymptomatic bacteriuria detected on routine post-treatment cultures—this contributes to antibiotic overuse 1
• Do not assume all dysuria in pregnancy is UTI—vaginal infections and other causes are common 4, 5
• Do not order repeat cultures in asymptomatic patients—this leads to detection and inappropriate treatment of colonization 3, 1

Patient Education

• Instruct the patient to seek prompt evaluation for any future febrile illness to ensure recurrent infections can be quickly detected 1
• Explain that negative culture means no bacterial infection requiring treatment
• Counsel on behavioral modifications if recurrent symptoms develop (adequate hydration, post-coital voiding) 3