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Wednesday, January 07, 2009

Meningitis in elderly all except HSV 2

Question 76
Meningitis in elderly all except
a.       Listeria
b.      Streptococcus Pneumonia
c.       Gram Negative
d.      HSV 2
Answer
d. HSV 2
Reference
Harrison 16th Edition Page 2471
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Discussion
·        S. pneumoniae is the most common cause of meningitis in adults >20 years. There are a number of predisposing conditions that increase the risk of pneumococcal meningitis, the most important of which is pneumococcal pneumonia. Additional risk factors include coexisting acute or chronic otitis media, alcoholism, diabetes, splenectomy, hypogammaglobulinemia, complement deficiency, and head trauma with basilar skull fracture and cerebrospinal fluid (CSF) rhinorrhea.
·        Enteric gram-negative bacilli are the causative organisms of meningitis that is associated with chronic and debilitating diseases such as diabetes, cirrhosis or alcoholism, and chronic urinary tract infections and following neurosurgical procedures, particularly craniotomy or craniectomy.
·        Resistance to infection with L. monocytogenes requires effective cell-mediated immunity. As a result, elderly individuals and those with impaired cell-mediated immunity due to organ transplantation, pregnancy, malignancy, chronic illness, or immunosuppressive therapy are all at increased risk for listerial meningitis. Infection is acquired by ingesting foods contaminated by this organism. Foodborne human listerial infection has been reported from contaminated coleslaw, milk, deli meat, and soft cheeses.
Explanatory
Self Explanatory
Comments
·        The frequency of H. influenzae type b meningitis in children has declined dramatically since the introduction of the Hib conjugate vaccine, although rare cases of Hib meningitis in vaccinated children have been reported. More frequently, H. influenzae causes meningitis in unvaccinated children and adults
·        Staphylococcus aureus and coagulase-negative staphylococci are predominant organisms causing meningitis that follows invasive neurosurgical procedures, particularly shunting procedures for hydrocephalus, or occurs as a complication of the use of subcutaneous Ommaya reservoirs for the administration of intrathecal chemotherapy
·        Etiology  Enteroviruses account for 75 to 90% of aseptic meningitis cases in most series. Viruses belonging to the Enterovirus genus are members of the family Picornaviridae and include the coxsackieviruses, echoviruses, polioviruses, and human enteroviruses 68 to 71. Using a variety of diagnostic techniques including CSF polymerase chain reaction (PCR) tests, culture, and serology, a specific viral cause can be found in 75 to 90% of cases of viral meningitis. CSF cultures are positive in 30 to 70% of patients, the frequency of isolation depending on the specific viral agent. Approximately two-thirds of culture-negative cases of aseptic meningitis have a specific viral etiology identified by CSF PCR testing (see below)
Tips
·        N. meningitidis accounts for nearly 60% of bacterial meningitis cases in children and young adults between the ages of 2 and 20. The nasopharynx is initially colonized by this organism, resulting in either an asymptomatic carrier state or invasive meningococcal disease. The risk of invasive disease following nasopharyngeal colonization depends on both bacterial virulence factors and host immune defense mechanisms, including the host's capacity to produce antimeningococcal antibodies and to lyse meningococci by both the classic and alternative complement pathways. Individuals with deficiencies of any of the complement components, including properdin, are highly susceptible to meningococcal infections.

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