Listeria monocytogenes is the only species of the genus Listeria that affects humans, mainly serotype 4b1. It is a small bacterium, of universal distribution, which acts as an intracellular pathogen. It is transmitted orally, from contaminated foods and after crossing the intestinal mucosa can produce systemic infections, with a predilection for the placental tissue and the consequent passage to the fetus, as well as the central nervous system.
The primary habitat of Listeria monocytogenes is vegetables, although, regarding oral transmission to humans, many foods have been involved: unpasteurized fresh cheeses, milk, prepared pork, and chicken dishes, undercooked meat, smoked fish, seafood, hot dogs, butter and salads. It is considered to be the third foodborne infection with the highest mortality, behind botulism and Vibrio vulnificus. Infections with Listeria monocytogenes usually appear sporadically in the community, mainly in the months of June, July, and August, although outbreaks have also been described, always in the form of febrile gastroenteritis (<1% of the total).
Listeriosis mainly affects newborns of colonized, pregnant, elderly and immunosuppressed mothers. It is very rare that it affects immunocompetent children outside the neonatal period, and the incidence of neonatal involvement is even decreasing due to the empiric treatment with ampicillin administered to pregnant women and to neonatal infectious risks.
However, the global incidence of listeriosis is increasing due to changes in food habits and food processing, the improvement of life expectancy and the increase in the number and survival of immunocompromised patients.
How Is Listeria Meningitis Treated?
There are no significant clinical features that differentiate Listeria meningitis from the rest of meningitis in pediatric patients; although in adults it is usually sub-acute. In addition, Listeria monocytogenes can cause encephalitis (the most frequent bacterial cause) and brain abscesses.
This diagnostic delay becomes important in that Listeria monocytogenes is not covered by the usual empirical treatment with cefotaxime and vancomycin since it is resistant to all cephalosporins. Initial improvement may appear in vivo due to vancomycin or corticosteroid treatment, with subsequent worsening.
The appropriate treatment for listeria meningitis is performed with intravenous ampicillin and gentamicin, with a controversial duration. In the clinical practice and in immunocompetent patients, the duration is usually 3 to 4 weeks in the case of involvement of the central nervous system. Occasionally, lumbar puncture will be repeated at the end of listeria meningitis treatment, and if the positivity of Listeria monocytogenes is maintained, treatment should continue until the negativity of the latter.
The first alternative treatment for listeria meningitis is trimethoprim-sulfamethoxazole. In vitro, imipenem, carbapenem, and linezolid also present good response; however, there is less clinical experience, and treatment failures with carbapenem have been described.
What is Meningitis?
Meningitis is the most relevant presentation and accounts for 5-10% of meningitis acquired in the community, with few cases published in immunocompetent patients.
Meningitis is the inflammation of the meninges, which are membranes that cover the entire central nervous system (brain and spinal cord) and the cerebrospinal fluid they contain. This inflammation can have various causes, although the most serious is meningococcal, a form of bacterial meningitis; although, it can also be caused by viruses, fungi, chemical agents, drugs, etc.
The most frequent symptoms are fever, headache, nausea, and vomiting. It may be accompanied by agitation, obtundation and decreased level of consciousness and the appearance of epileptic seizures and other signs of cerebral involvement. The most noteworthy fact in the physical examination is the stiffness of the neck flexion or neck stiffness. The transmission is different for each microorganism.
The diagnosis is compatible or confirmed by the growth of bacteria from cerebrospinal fluid or blood samples, by agglutination tests or by polymerase chain reaction (PCR). The identification of the serogroups and the susceptibility test to antibiotics are important to define the control measures. Proper treatment with antibiotics should be started as soon as possible, ideally after the lumbar puncture has been carried out.
In the face of a process of meningitis of torpid evolution, Listeria monocytogenes should be taken into account as an etiological agent, since it is a pathogenic microorganism of ascending and little-known incidence, not covered by the initial empirical antibiotic therapy and, although sporadically, can affect immunocompetent patients.
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