Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (114 page)

   Lymphocytic choriomeningitis virus: The virus is transmitted by the urine or feces of mice and other small rodents. There is an increased rate of infection during the winter months, presumably due to increased exposure. Aseptic meningitis caused by lymphocytic choriomeningitis is unusual because CSF may show decreased glucose concentrations and WBC counts >1,000/mm
³
. Diagnosis is usually established serologically.

   Mumps virus: Aseptic meningitis is a fairly frequent complication of mumps infection, but the incidence has significantly decreased due to effective vaccination programs. However, localized outbreaks continue to occur. This diagnosis may be suspected in patients with concurrent or recent parotitis.

Meningitis may be associated with CNS infection by parasitic, mycobacterial, fungal, and bacterial pathogens, as described in other sections. Other infectious agents to consider, based on clinical and laboratory findings, include

   Spirochetes (e.g.,
Treponema pallidum, Borrelia burgdorferi
)

   Tick-borne agents (e.g.,
Rickettsia
and
Ehrlichia
species)

   
Mycobacterium tuberculosis

   Fungal pathogens (
Cryptococcus neoformans, Coccidioides immitis
), especially in immunocompromised patients (see eBook Figure 4-37)

   Parasites: (e.g.,
Angiostrongylus
—suspect in patients with increased CSF eosinophils and risk based on epidemiology; amebas)

Aseptic meningitis may also be caused by malignancies, drugs, and other noninfectious causes.

Acute bacterial meningitis
(ABM) is a medical emergency (see eBook Figure 4-38). Outcome depends on early administration of effective antibiotics and appropriate medical and neurosurgical interventions. Overall,
N. meningitidis
and
S. pneumoniae
cause a majority of cases of ABM, but the etiology of ABM depends on multiple factors. Age and route of transmission are major determinants:

   Neonates (<1 month):
Streptococcus agalactiae, E. coli, Listeria monocytogenes
, other enteric gram-negative bacteria.
Elizabethkingia meningoseptica
has been associated with outbreaks of meningitis in neonatal inpatient settings.

   Infants (1–23 months):
S. pneumoniae, N. meningitidis, S. agalactiae, Haemophilus influenzae, E. coli
.

   Older children and adults (2–50 years):
N. meningitidis, S. pneumoniae.

   Elderly (>50 years):
N. meningitidis, S. pneumoniae, L. monocytogenes,
enteric gram-negative bacteria.

   Basilar skull fracture:
S. pneumoniae, Streptococcus pyogenes, H. influenzae.