A 10-month-old male infant is currently hospitalized on the pediatric ward. He was admitte… — USMLE Step 2 CK

A $10$ -month-old male infant is currently hospitalized on the pediatric ward. He was admitted $3$ days ago for severe respiratory syncytial virus (RSV) bronchiolitis requiring heated humidified high-flow nasal cannula. On hospital day $2$ , he developed a temperature of $39.5^\circ\text{C}$ ( $103.1^\circ\text{F}$ ), worsening hypoxemia, and new focal crackles in the left lower lung field. Chest radiography confirmed a new left lower lobe consolidation. Blood cultures were drawn, and empiric intravenous ceftriaxone was initiated for suspected secondary bacterial pneumonia. Today (hospital day $4$ ), he has been afebrile for $24$ hours and is weaning off respiratory support. Physical examination reveals scattered expiratory wheezing and mild intercostal retractions. The blood culture drawn on day $2$ is now positive for *Streptococcus pneumoniae*. Antimicrobial susceptibility testing indicates the isolate is susceptible to penicillin, ampicillin, ceftriaxone, and vancomycin. Which of the following is the most appropriate modification to this patient's treatment plan?

De-escalate antimicrobial therapy to intravenous ampicillinAnswer
B
Maintain the current regimen of intravenous ceftriaxone
C
Broaden antimicrobial coverage to intravenous vancomycin
D
Add scheduled treatments of nebulized albuterol
E
Initiate a short course of oral dexamethasone

Answer

De-escalate antimicrobial therapy to intravenous ampicillin

The correct intervention is to de-escalate antimicrobial therapy to intravenous ampicillin. This patient initially presented with viral bronchiolitis and subsequently developed a secondary bacterial pneumonia—a well-recognized complication of RSV infection. Empiric therapy with a broad-spectrum agent like ceftriaxone was appropriate initially to cover a wide range of potential pediatric respiratory pathogens. However, once blood cultures successfully identified *Streptococcus pneumoniae* that is susceptible to both penicillin and ampicillin, standard principles of antimicrobial stewardship dictate de-escalating to the narrowest-spectrum effective agent. Intravenous ampicillin is the preferred targeted therapy for susceptible *S. pneumoniae* pneumonia in the pediatric inpatient setting.

Step-by-Step Solution

Analyze the clinical course and culture results.

The patient has a primary viral bronchiolitis complicated by a secondary *Streptococcus pneumoniae* pneumonia. The bacterial isolate is susceptible to all tested penicillins and cephalosporins.

Establishing the definitive pathogen and its susceptibilities is required to optimize antimicrobial therapy.

Apply principles of antimicrobial stewardship to the current regimen.

The patient must be transitioned from empiric broad-spectrum coverage (ceftriaxone) to the narrowest-spectrum effective agent (ampicillin).

De-escalation minimizes the selective pressure for antimicrobial resistance and reduces the risk of adverse effects such as *C. difficile* infection.

Evaluate the clinical indication for asthma medications for the persistent wheezing.

Determine that bronchodilators and corticosteroids should be withheld.

Wheezing in bronchiolitis is caused by inflammation, mucosal edema, and cellular debris rather than smooth muscle bronchospasm, rendering asthma therapies ineffective.

Key Concept

Antimicrobial stewardship in secondary bacterial pneumonia and supportive management of viral bronchiolitis.

Estimated Time:1m 30s

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