Meningitis occurs as an extension of a variety of bacterial infections due to which of the following conditions?
A. Congenital anatomic abnormality of the meninges.
B. Lack of acquired resistance to the various etiologic organisms.
C. Occlusion or narrowing of the CSF pathway.
D. Natural affinity of the CNS to certain pathogens.
Correct Answer: B. Lack of acquired resistance to the various etiologic organisms.
Extension of a variety of bacterial infections is a major causative factor of meningitis and occurs as a result of a lack of acquired resistance to the etiologic organisms. Preexisting CNS anomalies are factors that contribute to susceptibility. Meningitis can be caused by infectious and non-infectious processes (autoimmune disorders, cancer/paraneoplastic syndromes, drug reactions). The infectious etiologic agents of meningitis include bacteria, viruses, fungi, and less commonly parasites.
Option A: The most common viral agents of meningitis are non-polio enteroviruses (group b coxsackievirus and echovirus). Other viral causes: mumps, Parechovirus, Herpesviruses (including Epstein Barr virus, Herpes simplex virus, and Varicella-zoster virus), measles, influenza, and arboviruses (West Nile, La Crosse, Powassan, Jamestown Canyon).
Option C: Organisms can enter the cerebrospinal fluid (CSF) via neighboring anatomic structures (otitis media, sinusitis), foreign objects (medical devices, penetrating trauma), or during operative procedures. Viruses can penetrate the central nervous system (CNS) via retrograde transmission along neuronal pathways or by hematogenous seeding.
Option D: Bacteria colonize the nasopharynx and enter the bloodstream after mucosal invasion. Upon making their way to the subarachnoid space, the bacteria cross the blood-brain barrier, causing a direct inflammatory and immune-mediated reaction.
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