An unvaccinated 7-month-old boy is evaluated in the pediatric clinic for a relentless coug… — USMLE Step 2 CK

An unvaccinated $7$ -month-old boy is evaluated in the pediatric clinic for a relentless cough. According to his parents, the illness started approximately $14$ days ago with mild nasal congestion and a low-grade fever. Over the past week, his cough has dramatically worsened into intense, rapid spasms. During these coughing fits, the infant becomes cyanotic around the mouth and frequently vomits his formula afterward. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), heart rate is $142/\text{min}$ , respiratory rate is $38/\text{min}$ , and oxygen saturation is $97\%$ on room air. On physical examination, the child appears well-nourished but has bilateral subconjunctival hemorrhages. Auscultation of the lungs reveals clear breath sounds bilaterally with no wheezing or crackles between coughing episodes. A complete blood count reveals a leukocyte count of $24,000/\text{mm}^3$ with $75\%$ lymphocytes. Which of the following is the most appropriate next step in management?

Azithromycin therapyAnswer
B
Supportive care and nasal suctioning
C
Nebulized albuterol and dexamethasone
D
Intravenous cefotaxime
E
Amoxicillin-clavulanate therapy

Answer

Azithromycin therapy

The correct intervention is azithromycin therapy. This patient's presentation of severe paroxysmal coughing, post-tussive emesis, cyanosis, subconjunctival hemorrhages, and marked lymphocytosis in the setting of missing immunizations is classic for 'whooping cough' caused by Bordetella pertussis. Macrolide antibiotics (e.g., azithromycin, clarithromycin) are the first-line treatment. While they may not significantly alter the clinical course if started late in the paroxysmal stage, they are critical for eradicating nasopharyngeal carriage and preventing transmission to close contacts.

Step-by-Step Solution

Analyze the patient's clinical presentation and immunization status.

The patient is an unvaccinated infant presenting with a two-week history of severe, paroxysmal coughing spells, post-tussive emesis, and facial cyanosis.

Identifying the characteristic symptoms (whooping cough spells, vomiting) in an unimmunized child raises strong suspicion for pertussis.

Interpret the physical exam and laboratory findings.

Clear lungs, subconjunctival hemorrhages (from severe coughing pressure), and marked leukocytosis with lymphocytosis (

24,000/\text{mm}^3

with

75\%

lymphocytes).

These findings are pathognomonic for Bordetella pertussis infection, differentiating it from typical viral respiratory infections which often present with wheezing or normal white blood cell counts.

Determine the most appropriate pharmacological intervention.

Macrolide antibiotics (such as azithromycin or clarithromycin) are the standard of care.

Macrolides effectively eradicate the bacteria from the nasopharynx, halting transmission. Early administration may also reduce symptom duration.

Key Concept

Bordetella pertussis presents with paroxysmal cough, post-tussive emesis, and marked lymphocytosis, and is treated with a macrolide antibiotic.

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