mrcp part 1 MCQ (SBA): Meningococcal Disease

A 19-year-old university student presents with a sudden onset of fever, severe headache, photophobia, and neck stiffness developing over the past 12 hours. On examination, he is drowsy, has a temperature of 39.2°C, and a widespread non-blanching petechial rash is noted on his trunk and limbs. What is the single most important immediate action in primary care or the emergency department?