## Clinical Diagnosis and Rationale This is a classic presentation of **pertussis (whooping cough)** in an incompletely vaccinated infant: - Paroxysmal cough with post-tussive vomiting (characteristic "whoop") - Inspiratory stridor (laryngeal involvement) - Afebrile status (typical in pertussis) - Age and vaccination history (only 1 of 3 primary doses) increase susceptibility ## Management Principles **Key Point:** Pertussis is a clinical diagnosis in the catarrhal and early paroxysmal stages. Culture confirmation takes 3–5 days; delaying antibiotics pending culture results increases risk of severe complications (apnea, seizures, secondary bacterial pneumonia) in infants <6 months. **High-Yield:** In infants <6 months with suspected pertussis, empiric antibiotic therapy is indicated immediately, regardless of culture status. Azithromycin is the first-line agent (10 mg/kg/day for 5 days). ## Isolation and Supportive Care **Clinical Pearl:** Pertussis is highly contagious (attack rate >90% in unvaccinated contacts). Respiratory isolation (negative-pressure room preferred) is mandatory until 5 days of appropriate antibiotics are completed. **Key Point:** Admission is indicated for: - Age <6 months (risk of apnea, cyanotic episodes, seizures) - Paroxysmal cough with post-tussive vomiting (aspiration risk) - Incomplete vaccination ## Why This Answer Is Correct Azithromycin + admission + isolation addresses: 1. Empiric treatment (clinical diagnosis sufficient) 2. Monitoring for life-threatening complications (apnea, bradycardia) 3. Infection control (negative-pressure isolation) 4. Supportive care (oxygen, suctioning, possible mechanical ventilation if needed)
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