Neonatal meningitis is an infection of the meninges and central nervous system (CNS) in the first month of life. This is the most common time of life for meningitis to occur.
The incidence is approximately 0.16 to 0.45 per 1000 live births in developed countries. The incidence may be higher in underdeveloped countries.
In most cases, infection occurs because of hematogenous seeding of the meninges and CNS. After attaching to the endothelium of the cerebral microvasculature and choroid plexus, bacteria can enter the cerebrospinal fluid (CSF) by several mechanisms including transcellular movement across the endothelial cell (eg, Escherichia coli), paracellular movement by disruption of intercellular tight junctions, and through transport across the blood–brain barrier within infected phagocytes (so-called “Trojan horse mechanism,” eg, Listeria monocytogenes). Inflammatory mediators are then released into the CSF in reaction to bacterial products, resulting in meningitis and increased permeability of the blood–brain barrier. In cases of CNS or spinal anomalies (eg, myelomeningocele), there may be direct inoculation by flora on the skin or in the environment. Neonatal meningitis is often accompanied by ventriculitis, which makes resolution of infection more difficult. There is also a predilection for vasculitis, which may lead to hemorrhage, thrombosis, and infarction. Subdural effusions and brain abscess may also complicate the course.
Most organisms implicated in neonatal sepsis also cause neonatal meningitis. Some have a definite predilection for CNS infection. Group B Streptococcus (GBS) (especially type III) and the gram-negative rods (especially E coli with K1 antigen) are the most common causative agents. GBS and E coli account for approximately two-thirds of all cases of neonatal meningitis. Galactosemia should be considered if E coli is the causative agent in late-onset meningitis. Multidrug-resistant E coli (eg, extended-spectrum β-lactamase producing) is an emerging problem in some neonatal units. Other causative organisms include L monocytogenes (serotype IVb), other streptococci (enterococci, Streptococcus pneumoniae), other gram-negative enteric bacilli (Klebsiella, Enterobacter, and Serratia spp), and rarely, Neisseria meningitides. In the very low birthweight (VLBW) infant, coagulase-negative staphylococci (CONS) need to be considered as causative organisms in bacterial meningitis.
With CNS anomalies involving open defects or indwelling devices (eg, ventriculoperitoneal shunts), staphylococcal disease (Staphylococcus aureus and Staphylococcus epidermidis) is more common, as is disease caused by other skin flora, including streptococci and diphtheroids. Many unusual organisms, including Ureaplasma, fungi, and anaerobes, have been described in case reports of neonatal meningitis.
Risk factors for neonatal meningitis are similar for neonatal sepsis and include low birthweight, prematurity, premature or prolonged rupture of membranes, septic or traumatic delivery, fetal hypoxia, maternal peripartum infection, and galactosemia. The characteristics of some bacteria make them more virulent, especially for neonates (eg, capsular polysaccharide of GBS type III, E coli K1, ...