A 21-year-old man is brought to the emergency department by his roommate due to worsening fever, headache, and confusion. The patient recently moved to a dormitory, and his prior medical problems and immunizations are unknown. Temperature is 39.2 C (102.6 F), blood pressure is 98/54 mm Hg, pulse is 112/min, and respirations are 24/min. The patient appears acutely ill. He is obtunded and has nuchal rigidity. Leukocyte count is 19,000/mm³ with 20% band neutrophils. Blood cultures are obtained and lumbar puncture is performed. Gram stain of cerebrospinal fluid reveals gram-negative cocci in pairs. Which of the following is the most likely way that this organism reached the meninges?

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11ec160b_3881_45c5_9249_cfe89f3ee90b_MD0001_00 Acute bacterial meningitis is a life-threatening infection that classically presents with the triad of fever, nuchal rigidity, and altered mental state. Most cases are caused by Streptococcus pneumoniae (gram-positive coccus) and Neisseria meningitidis (gram-negative diplococcus). These pathogens are transmitted via aerosolized droplets and are able to colonize the nasopharynx due to the presence of specialized surface components (eg, fimbriae, pili). Colonization usually leads to an asymptomatic carrier state, but in a minority of patients (~0.2%), the bacteria penetrate the epithelium and enter the bloodstream. Intravascular survival is dependent on capsular polysaccharides, which allow the bacteria to evade destruction by the alternative complement system. Meningitis occurs when the bacteria penetrate the cerebral capillary endothelium or the choroid plexus, the location of blood-CSF barrier. (Choice A) Haemophilus influenzae and S pneumoniae can rarely spread into the meninges from a middle ear infection. However, an ear infection is very uncommon cause of meningitis. (Choice C) Spread from the pharynx through the nasal lymphatics to the subarachnoid space may contribute to some cases of bacterial meningitis. However, this route is thought to be far less common than bloodstream invasion with subsequent hematogenous spread. (Choice D) Infections of the lung (eg, Mycobacterium tuberculosis, S pneumoniae) can lead to bacteremia and meningitis. However, N meningitidis does not usually colonize or infect the lung. (Choice E) Traumatic brain injury can lead to CSF leaks, with subsequent infection of the central nervous system. This is particularly common in the setting of basilar skull fracture. S pneumoniae (gram-positive cocci in pairs) is the most common organism. Educational objective: Neisseria meningitidis is transmitted primarily by aerosolized droplets and subsequently colonizes the nasopharyngeal epithelium. Penetration of the epithelium can lead to bloodstream infection. Spread to the meninges occurs via transcellular penetration of the cerebral capillary endothelium or entry at the choroid plexus.

A 21-Year-Old Man Is Brought to the Emergency Department by His