A 74-year-old woman is evaluated in the preoperative clinic 5 days before a scheduled righ… — USMLE Step 2 CK

A $74$ -year-old woman is evaluated in the preoperative clinic $5$ days before a scheduled right total knee arthroplasty. She has a history of severe osteoarthritis and chronic urge incontinence, which has been stable on a scheduled voiding regimen. The patient reports no new symptoms and specifically denies dysuria, urinary frequency, suprapubic discomfort, or flank pain. Her current medications include acetaminophen and cholecalciferol. Vital signs are within normal limits, including a temperature of $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ). Physical examination shows severe right knee crepitus and limited range of motion. There is no costovertebral angle or suprapubic tenderness. Preoperative laboratory results are as follows:

Leukocyte count: $7,800/\mu\text{L}$
Hemoglobin: $12.4$ g/dL
Platelets: $210,000/\mu\text{L}$

Urinalysis:
Color: Yellow
Appearance: Cloudy
Specific gravity: $1.018$
pH: $7.5$
Leukocyte esterase: Positive
Nitrites: Positive
WBC: $30$ /hpf
Bacteria: Many

A urine culture grows $>10^5$ CFU/mL of *Proteus mirabilis* that is susceptible to cefazolin, ceftriaxone, and ciprofloxacin. Which of the following is the most appropriate management of this patient's urinary findings prior to surgery?

A
Initiate a $5$ -day course of oral ciprofloxacin to be completed prior to surgery
B
Add a single dose of intravenous gentamicin in addition to standard surgical site prophylaxis
C
Postpone the surgery until a repeat urinalysis demonstrates resolution of pyuria
Proceed with the scheduled surgery without directed urinary antimicrobial therapyAnswer
E
Prescribe oral nitrofurantoin to begin on the morning of surgery and continue for $3$ days

Answer

Proceed with the scheduled surgery without directed urinary antimicrobial therapy.

This patient has asymptomatic bacteriuria (ASB), defined as the isolation of a specified quantitative count of bacteria in an appropriately collected urine specimen from a person without symptoms or signs referable to a urinary infection. According to current infectious disease and antimicrobial stewardship guidelines, screening and treatment for ASB are NOT recommended for most patients, including those undergoing orthopedic procedures with prosthetic hardware placement (e.g., total knee arthroplasty). The only standard indications for treating ASB are pregnancy, endoscopic urologic procedures involving mucosal trauma (e.g., transurethral resection of the prostate), and the early post-operative period following a renal transplant. Routine perioperative surgical prophylaxis is sufficient for this patient.

Step-by-Step Solution

Evaluate the patient's symptoms alongside the laboratory findings.

The patient has a positive urinalysis and urine culture (

>10^5

CFU/mL of *Proteus mirabilis*), but entirely denies urinary tract symptoms (no dysuria, frequency, or pain).

This clinical picture strictly defines asymptomatic bacteriuria (ASB) rather than a true urinary tract infection.

Determine the indications for treating asymptomatic bacteriuria.

Screening and treatment for ASB are only indicated in specific high-risk populations: pregnant women, patients undergoing endoscopic urologic procedures associated with mucosal trauma, and recent renal transplant recipients.

Applying evidence-based antimicrobial stewardship guidelines to prevent unnecessary antibiotic exposure.

Assess the planned surgical procedure.

The patient is undergoing a total knee arthroplasty, which is an orthopedic procedure involving hardware placement.

To verify if the procedure is an exception to the ASB guidelines. Evidence shows that treating ASB prior to orthopedic hardware placement does not reduce the incidence of prosthetic joint infections.

Select the most appropriate management plan based on stewardship principles.

The correct approach is to proceed with the scheduled surgery without directed urinary antimicrobial therapy. Standard perioperative surgical prophylaxis (e.g., intravenous cefazolin) is sufficient.

Unnecessary antibiotic therapy contributes to antimicrobial resistance and increases the risk of adverse events like *Clostridioides difficile* infection.

Key Concept

Management of asymptomatic bacteriuria prior to non-urologic surgery

Estimated Time:1m 30s

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