Background
Although the occurrence of neonatal meningitis is uncommon, it remains a devastating infection with high mortality and high morbidity. Neonatal meningitis is often caused by group B streptococcus and is associated with prematurity, gestational age, postnatal age, and geographic region. In order to improve prognosis of the infection, early diagnosis and prompt treatment are crucial to prevent mortality and the incidence of neurologic sequelae that cause long-term neurodevelopmental disabilities.
Despite the development of effective vaccines, useful tools for rapid identification of pathogens and potent antimicrobial drugs, neonatal meningitis continues to contribute substantially to neurological disability worldwide.
The persistence of neonatal meningitis results from increases in the numbers of infants surviving premature delivery and from limited access to medical resources in developing countries. In addition, the absence of specific clinical findings makes diagnosis of meningitis more difficult in neonates than in older children and adults. Moreover, a wide variety of pathogens are seen in infants as a consequence of the immaturity of their immune systems and intimate exposure to possible infection from their mothers.
This review focuses on common presentations of treatable bacterial and viral meningitis in the neonatal period, defined as the period from birth to 44 weeks after conception. Common central nervous system (CNS) infections caused by bacteria and viruses (eg, herpes simplex virus [HSV]) are emphasized. Meningitides caused by HIV and fungi are excluded, as are those caused by other organisms implicated in congenital CNS damage (eg, cytomegalovirus [CMV] and Toxoplasma).
For patient education resources, see the Brain and Nervous System Center, as well as Brain Infection.
Pathophysiology
Neonates are at greater risk for sepsis and meningitis than other age groups are because of the following deficiencies in humoral and cellular immunity and in phagocytic function:
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Inefficiency in the neonates’ alternative complement pathway compromises their defense against encapsulated bacteria [3]
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T-cell defense and mediation of B-cell activity are also compromised
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Deficient migration and phagocytosis by neutrophils contribute to neonatal vulnerability to pathogens of even low virulence [4]
Etiology
Common bacterial pathogens
Among US neonates, group B streptococci (GBS) are the most commonly identified causes of bacterial meningitis, implicated in roughly 50% of all cases. Escherichia coli accounts for another 20%. Thus, identification and treatment of maternal genitourinary infections is an important prevention strategy. [5] Listeria monocytogenes is the third most common pathogen, accounting for 5–10% of cases; it is unique in that it exhibits transplacental transmission. [6]
Studies suggest that in underdeveloped countries, gram-negative bacilli—specifically, Klebsiella organisms and E coli —may be more common than GBS. In a series from Africa and South Asia, Tiskumara et al noted that 75% of cases of late-onset meningitis were due to gram-negative bacilli. [7] In a review of studies from Asia, Africa, and Latin America, Zaidi et al reported that the most common organisms were Klebsiella species, E coli, and Staphylococcus aureus. [8]
With the widespread use of intrapartum antibiotic prophylaxis since 1996 in developed countries, the incidence of early-onset GBS infection has decreased, whereas the incidence of late-onset disease has remained fairly constant. [9] However, from 2003 to 2006, the Centers for Disease Control and Prevention (CDC) reported a slight increase in early-onset disease in the United States, particularly in the African American population; the reasons for this are unclear. [10]
Herpes simplex virus
As many as 95% of viral infections caused by HSV result from intrapartum transmission, with occasional postnatal exposure occurring through oropharyngeal shedding or cutaneous shedding of virus by parents or hospital contacts. Late presentation in the second postnatal week is more commonly seen than early presentation of disseminated disease.
Emerging pathogens
As cases of neonatal enteroviral sepsis and aseptic meningitis come to be more frequently recognized, reporting and identification of more virulent serotypes as they affect infants are likely to play a growing role. [11] As many as 12% of neonates may be infected with this family of viruses. Although many of these babies are asymptomatic, enterovirus may be responsible for as many as 3% of neonates who present with a sepsislike picture. [12] More recently, human parechovirus-3 has been implicated in an increasing number of neonates with meningitis. While related to the enterovirus family, this pathogen is not detected with enteroviral polymerase chain reaction (PCR) studies performed on cerebrospinal fluid (CSF). [13, 14]
Enterobacter sakazakii has been identified as an emerging pathogen in neonates. This bacterium is most typically associated with the ingestion of contaminated reconstituted formula. It has been reported with increasing frequency in the past few years, prompting the US Food and Drug Administration (FDA) to publish warnings of possible contamination of dried formula. [15]
Epidemiology
Geographic region is a significant factor in the occurrence of neonatal meningitis. Due to the lack of resources and access to health care in developing countries, the incidence of neonatal meningitis is much higher as compared to developed countries. [41]
Due to the progress of medicine in developed countries, the incidence of neonatal meningitis is estimated to be 0.3 per 1000 live births, as observed in the United States, Sweden, The Netherlands, England, and Wales. [4] The incidence of HSV meningitis is estimated to be 0.02–0.5 cases per 1000 live births. [16] Because of testing limitations, the worldwide incidence of neonatal meningitis is difficult to determine with accuracy. However, a study of neonatal infections in Asia (based on data collected from China, Hong Kong, India, Iran, Kuwait, and Thailand) reported estimated incidences of neonatal meningitis that ranged from 0.48 per 1000 live births in Hong Kong to 2.4 per 1000 live births in Kuwait. [7] Another publication that looked at neonatal infections in Africa and South Asia reported figures ranging from 0.8 to 6.1 per 1000 live births. [17]
These numbers are believed to underestimate the true incidence of neonatal meningitis in underdeveloped countries, given the lack of access to health care facilities in these areas.
Prognosis
Survivors of neonatal meningitis are at significant risk for moderate to severe disability. Some 25-50% have significant problems with language, motor function, hearing, vision, and cognition [18, 3] ; 5-20% have future epilepsy. [19, 20] Survivors are also more likely to have subtle problems, including visual deficits, middle-ear disease, and behavioral problems. [21] As many as 20% of children identified as normal at 5-year follow-up may have significant educational difficulties lasting into late adolescence. [18]
Poor prognostic indicators include low birth weight, prematurity, significant leukopenia or neutropenia, high levels of protein in the cerebrospinal fluid (CSF), delayed sterilization of the CSF, and coma. [1, 2] Seizures lasting longer than 72 hours and the need for inotropes predict moderate-to-severe disability or death with 88% sensitivity and 99% specificity. [5]
Bacterial meningitis
In developed countries, mortality from bacterial meningitis among neonates declined from almost 50% in the 1970s to less than 10% in the late 1990s. However, a corresponding decrease in morbidity rate did not occur. [9]
In a prospective sample of more than 1500 neonates surviving to the age of 5 years, the prevalence of motor disabilities (including cerebral palsy) was 8.1%, that of learning disability was 7.5%, that of seizures was 7.3%, and that of hearing problems was 25.8%. [21] No problems were reported in 65% of babies who survived GBS meningitis and in 41.5% of those who survived E coli meningitis.
HSV meningitis
Mortality among neonates with HSV infection of the CNS is 15%. Of these cases, 25-40% will have culture-proven CSF infection. The 2 HSV serotypes (HSV-1 and HSV-2) carry the same risk of mortality. However, HSV-2 is more commonly associated with morbidity, including cerebral palsy, intellectual disability, seizures, microcephaly, and ophthalmic defects. [16] Although the use of acyclovir has reduced the morbidity and mortality associated with HSV infection, neurological sequelae are likely in 50% of neonates with HSV meningitis. [16]
Patient Education
It is encouraged that pregnant mothers undergo prenatal screening and are administered a group B Streptococcus vaccine to combat the risk of neonatal meningitis. Since this infection is so lethal, prevention is the primary approach and this is optimized by the utilization of vaccines against group B Streptococcus.
Since listeria is another bacteria known to cause neonatal meningitis, pregnant mothers should avoid foods that have the potential to be contaminated by listeria. This includes processed meat, soft cheese, coleslaw, and paté [42] . Listeria monocytogenes can be transmitted transplacentally, so pregnant mothers should be aware of the types of food that they are eating.
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Acute bacterial meningitis (same patient as in the other two images). This axial nonenhanced CT scan shows mild ventriculomegaly and sulcal effacement.
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Acute bacterial meningitis (same patient as in the other two images). This axial T2-weighted MRI shows only mild ventriculomegaly
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Acute bacterial meningitis (same patient as in the other two images). This contrast-enhanced, axial T1-weighted MRI shows leptomeningeal enhancement (arrows).
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Meninges of the central nervous parts
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Neisseria meningitidis
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Neonate with a lumbar myelomeningocele with an L5 neurologic level. Note the diaphanous sac filled with cerebrospinal fluid and containing fragile vessels in its membrane. Also, note the neural placode plastered to the dorsal surface of the sac. This patient underwent closure of his back and an untethering of his neural placode. The neural placode was circumnavigated and placed in the neural canal. A dural sleeve was fashioned in such a way to reconstruct the neural tube geometry.
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This anteroposterior skull radiograph demonstrates the craniolacunia or Luckenschadel seen in patients with myelomeningocele and hydrocephalus. Mesodermal dysplastic changes cause defects in the bone. The thin ovoid areas of calvaria are often surrounded by dense bone deposits. They are most likely the result of defective membranous bone formation typical of neural tube defects and not increased intracranial pressure as once thought. These characteristic honeycomb changes are seen in about 80% of the skulls in children with myelomeningocele and hydrocephalus
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Sagittal T1-weighted MRI image of a child after closure of his myelomeningocele. Child is aged 7 years. Note the spinal cord ends in the sacral region far below the normal level of T12-L1. It is tethered at the point in which the neural placode was attached to the skin defect during gestation. The MRI showed dorsal tethering, and the child complained of back pain and had a new foot deformity on examination. By definition, all children with a myelomeningocele have a tethered cord on MRI, but only about 20% of children require an operation to untether the spinal cord during their first decade of life, during their rapid growth spurts. Thus, the MRI must be placed in context of a history and examination consistent with mechanical tethering and a resultant neurologic deterioration.
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Sagittal T1 MRI image of a child with a myelomeningocele and associated Chiari II malformation. Note the cerebellar vermis and part of the brainstem has herniated below the foramen magnum and into the cervical canal (arrow). This patient had multiple brainstem symptoms and findings to include stridor and cranial nerve paresis (cranial nerves III, VI, IX, X) despite having a well-functioning ventricular-peritoneal shunt. He required a posterior fossa decompression of his hindbrain in order to relieve the symptoms of hindbrain herniation and brainstem compression. A minority of myelomeningocele patients require a Chiari II decompression. Those that do usually present in their first year of life with similar symptoms, stridor and cranial nerve paresis. A functioning shunt is imperative prior to exploring the posterior fossa in these children. Often times, especially in older children, a shunt revision may alleviate some of the symptoms of hindbrain compression. Tube Defects in the Neonatal Period
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Neonate with a large occipital encephalocele lying in the prone position prior to surgical intervention. Note the large skin-covered sac that represents a closed neural tube defect. Often called cranium bifidum, it is a more serious condition that represents a failure of the anterior neuropore to close. In this patient, a defect in the skull base (basicranium) was associated with this large sac filled with cerebrospinal fluid and a small, disorganized remnant of brain. The patient fared satisfactorily after the surgery in which the encephalocele was excised. However, the patient needed placement of a ventricular-peritoneal shunt to treat the resultant hydrocephalus, which is not uncommon. At age 5 years, the child was doing well and had only moderate developmental delay.
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Autopsy specimen on a child with anencephaly. This is one of the most common CNS malformations in the West. The neonate, like almost all with such a severe forms of neural tube defects, did not survive more than a few hours or days. This malformation represents a failure of the anterior neuropore to close. This photograph also reveals an absence of the calvaria and posterior bone elements of the cervical canal, as well as the deficiency in the prosencephalon. Photo courtesy of Professor Ron Lemire.
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Ventral view of a child with anencephaly that, like the previous picture, shows the loss of cranium and enclosed nervous tissue. In addition to the primary defect in development, a secondary destruction of nervous tissue occurs. Direct exposure to the caustic amniotic fluid causes progressive destruction of the remaining neural structures and secondary proliferation of a thin covering of vascular and glial tissue. Photo courtesy of Professor Ron Lemire.
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These 2 photographs depict the lumbar regions on 2 different children with closed neural tube defects. Both children have lipomyelomeningocele. The child in the left has a dorsal lipoma that is pedunculated. The child on the right has a more common-appearing lipomatous mass that is heaped up beneath the skin. Both lipomas lead from the subcutaneous tissue, through the dura and into the intradural space, where they are attached to the spinal cord. Photos courtesy of Professor J.D. Loeser.
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Photograph of a child undergoing a neurosurgical procedure in which the spinal cord is being detached (untethered) from the intradural and extradural lipomatous mass that fixes it to the subcutaneous tissue. The white arrow shows the laser char on the lipoma that has been shaved off the spinal cord and was connected to the extradural mass. The black arrow shows the extradural lipoma, which crept through the dura and attached to the spinal cord, thereby firmly fixing the spinal cord at too low and too dorsal a location in the sagittal plane.
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The lumbar region of a newborn baby with myelomeningocele. The skin is intact, and the placode-containing remnants of nervous tissue can be observed in the center of the lesion, which is filled with cerebrospinal fluid (CSF).
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Axial T1-weighted MRI scan of an 8-week-old girl who presented with enlarging head circumference. Considerable ventricular dilatation is shown on the lateral and third ventricles. Periventricular lucency is observed around the frontal horns, indicating raised intraventricular pressure.
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Sagittal T1-weighted MRI scan of an 8-week-old girl who presented with enlarging head circumference. The third and lateral ventricles are dilated, whereas the fourth ventricle is of normal size. Aqueductal stenosis is shown. The appearance is typical of this condition.
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Phase-contrast MRI scan of an 8-week-old girl who presented with enlarging head circumference, obtained 3 months after endoscopic third ventriculostomy. A large signal void is shown in the prepontine region, corresponding to the flow through the stoma in the floor of the third ventricle, indicating that the ventriculostomy is functioning well.
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Axial T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. She was treated with a ventriculoperitoneal shunt. The ventricular system has a characteristic shape, with small frontal and large occipital horns, which are typical in patients with spina bifida. The shunt tube is shown in the right parietal region.
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Sagittal T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. Significant hindbrain hernia and low-lying fourth ventricle are shown in the context of the Arnold-Chiari II syndrome. Damaged shunt valve removed during shunt revision from a 22-year-old woman with hydrocephalus and spina bifida. The material of the valve has dramatically disintegrated.
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Damaged shunt valve removed during shunt revision from a 22-year-old woman with hydrocephalus and spina bifida. The material of the valve has dramatically disintegrated.
