A 6-month-old boy is brought to the pediatric clinic by his parents due to a worsening cou… — USMLE Step 2 CK

A $6$ -month-old boy is brought to the pediatric clinic by his parents due to a worsening cough. For the past week, he had a mild runny nose and low-grade fever. Over the last $48$ hours, the cough has become severe, occurring in intense spasms. The parents note that he occasionally vomits immediately after these coughing spells and his face turns red during the episodes. He has only received his first set of immunizations at $2$ months of age due to parental hesitancy. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $90/55\text{ mmHg}$ , pulse is $135/\text{min}$ , and respirations are $42/\text{min}$ . Pulse oximetry shows $98\%$ on room air. The patient appears comfortable and playful in the examination room. Cardiopulmonary examination reveals clear lungs bilaterally without crackles or wheezes. Laboratory testing shows a leukocyte count of $24,000/\text{mm}^3$ with $78\%$ lymphocytes. Which of the following is the most appropriate next step in management?

Prescribe oral azithromycinAnswer
B
Administer nebulized albuterol
C
Admit to the hospital and start intravenous ceftriaxone
D
Prescribe oral amoxicillin
E
Administer the measles, mumps, and rubella (MMR) vaccine

Answer

Prescribe oral azithromycin

The patient's clinical presentation—intense coughing spasms, post-tussive emesis, facial plethora during episodes, and marked lymphocytosis—in the setting of incomplete immunizations is classic for Bordetella pertussis infection. The paroxysmal stage typically follows a 1- to 2-week catarrhal phase (mild URI symptoms). Azithromycin (or another macrolide) is the first-line treatment. Although antibiotic therapy initiated during the paroxysmal phase may not significantly alter the clinical course of the disease, it is critical for eradicating the bacteria from the nasopharynx, thereby decreasing infectivity and preventing transmission to others. Because the infant is well-appearing between spells and maintains normal oxygenation on room air, outpatient management with oral antibiotics is safe and appropriate.

Step-by-Step Solution

Analyze the clinical presentation and immunization history.

The patient is an under-immunized 6-month-old infant with a paroxysmal cough, post-tussive emesis, and marked lymphocytosis.

These classic findings strongly suggest an infection with Bordetella pertussis (whooping cough).

Assess the severity of the illness.

The infant is well-appearing between coughing fits, has normal vital signs for his age, and maintains normal oxygen saturation on room air.

This indicates that the patient is hemodynamically and clinically stable enough for outpatient management rather than requiring hospital admission.

Determine the appropriate pharmacotherapy.

Select a macrolide antibiotic such as azithromycin.

Macrolides are the first-line treatment for pertussis. They eradicate the organism from the nasopharynx to prevent transmission and, if given early enough, may reduce the duration of symptoms.

Key Concept

Diagnosis and management of Bordetella pertussis in an incompletely immunized infant

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