Listeria monocytogenes meningitis in the elderly: Epidemiological, clinical and therapeutic findings

Listeria monocytogenes is a Gram-positive bacillus and facultative intracellular bacterium whose transmission occurs mainly through the consumption of contaminated food, L. monocytogenes invades the host cells using various protein and can escape to the human T-cell immune system by cell-to-cell spreading. If the infection is not controlled at the stage in which the bacterium is in the liver, for instance, due to a severe immunodepression, a secondary bacteraemia can be developed and L. monocytogenes reaches the preferred sites transgressing the blood-brain barrier or the placental barrier. Individuals with T-cell dysfunction, such as pregnant women, the elderly, and those receiving immunosuppressive therapy are at the highest risk of contracting the disease. Average life expectancy throughout developed countries has rapidly increased during the latter half of the 20th century and geriatric infectious diseases have become an increasingly important issue. L. monocytogenes meningitis in young previously healthy adults has been reported only in anecdotal observations. Differently, L. monocytogenes is the third most common cause of bacterial meningitis in the elderly population, after Streptococcus pneumoniae and Neisseria meningitidis. Patients with L. monocytogenes meningitis presented with signs and symptoms that were similar to thoseof the general population with community-acquired bacterial meningitis, but reported a longer prodromal phase. According to literature data, the prevalence of the classic triad of fever, neck stiffness, and altered mental status is 43%, and almost all patients present with at least 2 of the 4 classic symptoms of headache, fever, neck stiffness, and altered mental status. On the basis of our published data, in patients aged over 50 years, diagnosing L. monocytogenes meningitis was more challenging than pneumococcal meningitis, as demonstrated by the lower percentage of cases receiving a correct diagnosis within 48 hours from the onset of symptoms. No significant difference was observed in respect to the presenting symptoms, but progression to respiratory failure was not as rapid as pneumococcal meningitis. Findings of cerebrospinal-fluid (CSF) analysis demonstrated higher glucose concentration and a less evident neutrophil prevalence in patients with L. monocytogenes meningitis. Meningitis sustained by L. monocytogenes is reported with a higher frequency in elderly, clinical findings cannot support a presumptive diagnosis, but findings of CSF analysis have to be considered.