A 78-year-old man is brought to the emergency department from a skilled nursing facility d… — USMLE Step 2 CK

A $78$ -year-old man is brought to the emergency department from a skilled nursing facility due to a $2$ -day history of progressively worsening confusion, profound lethargy, and severe constipation. His past medical history is significant for advanced prostate cancer with known bone metastases, benign prostatic hyperplasia, and the presence of a chronic indwelling urethral catheter.

Upon arrival, his temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $136/84\text{ mm Hg}$ , pulse is $76/\text{min}$ , and respirations are $14/\text{min}$ . He is difficult to arouse but oriented to person when awakened. Physical examination reveals markedly dry mucous membranes and poor skin turgor. His abdomen is soft and non-tender, and there is no costovertebral angle or suprapubic tenderness.

Laboratory evaluation shows:
- Leukocyte count: $8,200/\text{mm}^3$
- Hemoglobin: $10.4\text{ g/dL}$
- Serum creatinine: $1.8\text{ mg/dL}$ (baseline $1.0\text{ mg/dL}$ )
- Blood urea nitrogen: $42\text{ mg/dL}$
- Serum calcium: $13.8\text{ mg/dL}$
- Serum albumin: $3.5\text{ g/dL}$

Urinalysis reveals cloudy urine with positive leukocyte esterase, positive nitrites, and $45-50\text{ white blood cells/hpf}$ .

The patient is admitted and aggressively treated with intravenous normal saline and calcitonin, resulting in a rapid improvement in his mental status over the next $24$ hours. However, a urine culture obtained at the time of admission now grows $>10^5\text{ CFU/mL}$ of *Escherichia coli*. The isolate is resistant to ciprofloxacin but susceptible to ceftriaxone, cefepime, and meropenem.

Which of the following is the most appropriate next step in the management of this patient's urinary findings?

A
Initiate intravenous ceftriaxone
B
Initiate intravenous cefepime
Observation without antibiotic therapyAnswer
D
Exchange the urinary catheter and initiate oral fosfomycin
E
Initiate intravenous meropenem

Answer

Observation without antibiotic therapy

The correct approach is observation without antibiotic therapy because this patient has asymptomatic bacteriuria (ASB). Although he initially presented with confusion—a common atypical presentation of infection in older adults—his delirium was entirely explained by severe hypercalcemia (

13.8\text{ mg/dL}

) secondary to his advanced prostate cancer and bone metastases. This is confirmed by the fact that his mental status rapidly improved with aggressive hydration and calcitonin, prior to the initiation of any antimicrobial therapy. The patient has no fever, no leukocytosis, and no localizing genitourinary symptoms. In patients with a chronic indwelling Foley catheter, colonization with bacteria is virtually universal, and pyuria is expected due to foreign body irritation of the uroepithelium. Therefore, neither a positive urinalysis nor a positive culture distinguishes ASB from a true catheter-associated urinary tract infection (CAUTI). In the absence of signs of systemic infection or local symptoms, antimicrobial treatment is strictly contraindicated as it does not improve clinical outcomes and actively contributes to antimicrobial resistance and adverse events.

Step-by-Step Solution

Analyze the patient's initial presentation and laboratory results.

The patient presented with confusion, dehydration, and severe hypercalcemia (

13.8\text{ mg/dL}

), alongside normal vital signs and a normal leukocyte count.

To identify the primary physiologic derangement causing the altered mental status.

Evaluate the clinical course following initial intervention.

The patient's confusion rapidly completely resolved after hydration and calcium-lowering therapy.

To determine definitively if the altered mental status was caused by the metabolic abnormality rather than an underlying occult infection.

Interpret the urinalysis and urine culture results in the context of the clinical picture.

The patient has bacteriuria and pyuria, but no systemic signs of infection and a clear non-infectious etiology for his initial delirium.

To differentiate between asymptomatic bacteriuria (ASB) and a catheter-associated urinary tract infection (CAUTI).

Determine the appropriate management for asymptomatic bacteriuria.

Antibiotic therapy is withheld and observation is continued.

Treating ASB provides no clinical benefit and directly increases the risk of adverse drug effects and antimicrobial resistance.

Key Concept

Asymptomatic bacteriuria in patients with chronic indwelling catheters should not be treated with antibiotics, even in the presence of pyuria, unless there are systemic signs of infection or localizing symptoms that cannot be attributed to another cause.

Estimated Time:1m 30s

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