A 3-year-old child presents with a 2-day history of high fever, irritability, and a non-blanching rash that started on the trunk and spread to the extremities. He had a preceding upper respiratory infection a week ago. On examination, he is lethargic, has nuchal rigidity, and petechiae are noted over his trunk and limbs. Lumbar puncture reveals elevated white blood cells with neutrophil predominance, elevated protein, and low glucose. What is the most likely causative organism?

The correct answer to the question "A 3-year-old child presents with a 2-day history of high fever, irritability, and a non-blanching rash that started on the trunk and spread to the extremities. He had a preceding upper respiratory infection a week ago. On examination, he is lethargic, has nuchal rigidity, and petechiae are noted over his trunk and limbs. Lumbar puncture reveals elevated white blood cells with neutrophil predominance, elevated protein, and low glucose. What is the most likely causative organism?" is Option C: Neisseria meningitidis.

The other options — A) Streptococcus pneumoniae, B) Haemophilus influenzae, D) Escherichia coli — are incorrect for this USMLE Exam Prep question. As explained above: The presentation of fever, nuchal rigidity, lethargy, and a petechial rash following a URI, especially in a child, is highly suggestive of meningococcal meningitis caused by Neisseria meningitidis. T…