A 76-year-old woman is evaluated in the clinic prior to an elective right total knee arthr… — USMLE Step 2 CK

A 76-year-old woman is evaluated in the clinic prior to an elective right total knee arthroplasty scheduled for the following week. She has a history of osteoarthritis and well-controlled essential hypertension. She reports no new symptoms and specifically denies dysuria, urinary frequency, urgency, suprapubic pain, fever, or chills. Her temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $128/78\text{ mm Hg}$ , and pulse is $76/\text{min}$ . Physical examination of the abdomen and costovertebral angles is unremarkable. As part of her preoperative evaluation, a urinalysis is obtained which shows $15$ white blood cells/hpf and is positive for leukocyte esterase and nitrites. A subsequent urine culture grows $>10^5\text{ CFU/mL}$ of Escherichia coli that is susceptible to ceftriaxone, ciprofloxacin, trimethoprim-sulfamethoxazole, and nitrofurantoin. Which of the following is the most appropriate management regarding these laboratory findings?

A
Postpone the surgical procedure until a repeat urine culture is negative
B
Administer a single dose of intravenous ceftriaxone preoperatively
Proceed with the scheduled surgery without prescribing antimicrobial therapyAnswer
D
Prescribe a course of oral nitrofurantoin prior to the procedure
E
Prescribe a course of oral ciprofloxacin prior to the procedure

Answer

Proceed with the scheduled surgery without prescribing antimicrobial therapy

The correct answer correctly identifies that this patient has asymptomatic bacteriuria (ASB), defined as the presence of bacteria in the urine without accompanying signs or symptoms of a urinary tract infection. In the general population, including the elderly, ASB is common and does not lead to adverse outcomes. According to current guidelines, screening for and treating ASB is strictly limited to specific high-risk scenarios: pregnant women, patients undergoing urologic procedures with anticipated mucosal bleeding (e.g., transurethral resection of the prostate), and patients who have recently received a renal transplant. For patients undergoing non-urologic procedures—including orthopedic procedures involving hardware such as a total knee arthroplasty—treating ASB does not decrease the rate of surgical site infections. Therefore, administering antibiotics for the urinary findings is inappropriate and constitutes poor antibiotic stewardship, as it unnecessarily risks adverse drug effects and promotes microbial resistance.

Step-by-Step Solution

Analyze the patient's clinical presentation and laboratory findings.

The patient has pyuria and bacteriuria on urinalysis and culture, but completely lacks genitourinary symptoms (no dysuria, frequency, or fever).

Establishing the presence or absence of symptoms is required to differentiate between a symptomatic urinary tract infection and asymptomatic bacteriuria (ASB).

Determine the indications for treating asymptomatic bacteriuria.

Current guidelines recommend treating ASB only in pregnant women, patients undergoing urologic procedures with anticipated mucosal bleeding, and recently placed renal transplants.

To decide if the positive urine culture requires targeted antimicrobial therapy prior to her scheduled orthopedic surgery.

Formulate the most appropriate management plan.

The surgery should proceed as scheduled without prescribing antibiotics directed at the urine culture findings.

Treating ASB prior to orthopedic surgery, including total joint arthroplasty, does not reduce the risk of prosthetic joint infections and unnecessarily increases the risk of antimicrobial resistance.

Key Concept

Asymptomatic bacteriuria (ASB) screening and treatment are not indicated prior to non-urologic surgical procedures, including orthopedic surgeries like total joint arthroplasty.

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