Chapter 50 Meningitis
PATHOPHYSIOLOGY
Meningitis is an acute inflammation of the meninges. The organisms responsible for bacterial meningitis invade the area either directly as a result of a traumatic injury or indirectly when they are transported from other sites in the body to the cerebrospinal fluid (CSF). A variety of agents can produce an inflammation of the meninges including bacteria, viruses, fungi, and chemical substances.
Since the introduction and widespread use of the Haemophilus influenzae type B (HIB) vaccine, this organism has been largely controlled in the developed world. The principal bacterial pathogen in children and adults is Streptococcus pneumoniae, followed by Neisseria meningitidis. In infants 0 to 3 months of age, the most common causes are group B Streptococcus, Escherichia coli, and Listeria monocytogenes.
Aseptic meningitis is usually caused by enteroviruses and affects young adults more often than children. Older children usually manifest a variety of nonspecific prodromal signs and flulike symptoms that last for 1 to 2 weeks. Although fatigue and weakness may persist for a number of weeks, sequelae are uncommon. The child is evaluated and treated until bacterial meningitis is ruled out. Viral meningitis usually requires only a brief hospitalization; supportive care at home is the primary intervention.
Otitis media, sinusitis, or respiratory tract infections may constitute the initial stage of infection. Newer technology, such as cochlear implants, may also lead to meningitis. Head injuries, penetrating wounds, and neurosurgery may also provide an opening into the meninges, leading to meningitis. In addition, a predisposition resulting from an immune deficiency increases the likelihood of occurrence of this disorder. Once the meninges are infected, the organisms are spread through the CSF to the brain and adjacent tissues.
Prognosis varies depending on the individual’s age, the infecting organism, the speed with which antibiotic therapy is initiated, and the presence of complicating factors. Neonatal meningitis is associated with a high mortality rate and an increased incidence of neurologic sequelae. Meningococcal meningitis can also be rapidly fatal. In many affected individuals, bacterial meningitis can result in long-term behavioral changes, motor dysfunction, hearing loss, and cognitive changes such as perceptual deficits and learning disorders.
Ensuring vaccination with HIB vaccine during the infant and toddler years, and meningococcal vaccine during preteen years or before college entry can go a long way in prevention of meningitis. All children with cochlear implants should also receive pneumococcal vaccine to prevent meningitis caused by S. pneumoniae. Children with immune deficiencies are also recommended to have these vaccines.
INCIDENCE
1. Of all bacterial meningitis cases, 90% are in children younger than 5 years of age.
2. More males than females contract meningitis.
3. Age range of peak incidence is 6 to 12 months.
4. Age range with the highest rate of morbidity is birth to 4 years.
5. Meningitis occurs mostly during winter and early spring.
6. About 171,000 people worldwide die from bacterial meningitis yearly.
