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 ∼0.16–0.45 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. 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 Escherichia coli with K1 antigen) are the most common causative agents. Galactosemia should be considered if E. coli is the causative agent in late-onset meningitis. Other causative organisms include Listeria 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 infant, coagulase-negative staphylococci 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.
Premature infants with sepsis have a much higher incidence (up to 3-fold) than term infants of CNS infection. The characteristics of some bacteria make them more virulent, especially for neonates (eg, capsular polysaccharide of GBS type III, E. coli K1, and L. monocytogenes serotype IVb all contain sialic acid in high concentrations). Infants with CNS defects necessitating ventriculoperitoneal shunt procedures also are at increased risk.
The clinical presentation is usually nonspecific and indistinguishable from those caused by sepsis. Meningitis must be excluded in any infant being evaluated for sepsis or infection. Signs and symptoms of meningitis include temperature instability (the most common), lethargy, irritability, poor tone, seizures, feeding intolerance, vomiting, respiratory distress, apnea, or cyanotic episodes. Seizures, often focal, can be the presenting manifestation in up to 50% of the cases. Late manifestations of meningitis include a bulging anterior fontanelle and coma. Syndrome of inappropriate antidiuretic hormone may accompany meningitis.