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CENTRAL NERVOUS SYSTEM INFECTIONS

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Acute Bacterial Meningitis Beyond the Neonatal Period

XAVIER SÁEZ-LLORENS
GEORGE H. McCRACKEN JR.

ETIOLOGIC AGENTS AND EPIDEMIOLOGY
In otherwise healthy children, the three most common organisms causing hematogenously acquired acute bacterial meningitis are Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b (Hib). Although Hib was by far the most common bacterial cause before availability of the Hib conjugate vaccine, the current likelihood of Hib meningitis in a child who has received at least two doses of vaccine is extraordinarily lower. In surveillance studies conducted by the Centers for Disease Control and Prevention (CDC), the incidence of Hib disease declined by 95% from 1987 to 1993 in children younger than 5 years (41 cases per 100,000 in 1987 to 2 per 100,000 in 1993) ( Fig. 41–1 ).[1] Similar data from 1997 indicated a further decline to 1.3 cases per 100,000 (97% reduction).[2]
Meningitis due to Hib has a peak incidence in the fall and winter and occurs more commonly in blacks. Pneumococcal meningitis and meningococcal meningitis also occur more commonly during the winter; meningococcal disease can be endemic or epidemic. The annual

 Figure 41-1 Incidence of invasive Haemophilus influenzae disease among children younger than 5 years and the number of states reporting H. influenzae surveillance data to the National Notifiable Diseases Surveillance System, 1987–1994, United States. Insert represents the incidence of invasive H. influenzae disease among persons 5 years or older. Rate is expressed as cases per 100,000 population. (From Centers for Disease Control and Prevention. Progress toward elimination of Haemophilus influenzae type b disease among infants and children—United States, 1983–1994. MMWR 1995;44:545.)
incidence of bacterial meningitis in children younger than 5 years, as assessed by the CDC, has been relatively stable for both N. meningitidis (about 4 to 5 cases per 100,000) and S. pneumoniae (about 2.5 per 100,000) since 1980. Seven of the >90 pneumococcal serotypes (4, 6B, 9, 14, 18F, 19F, and 23F) account for >80% of invasive disease in children from developed countries; serotypes 5 and 1 are also prevalent in developing countries.[3] Serogroups B and C are the most common serogroups of N. meningitidis causing invasive infections in the American continent, although group Y strains now account for 20% to 25% of cases.
Children with a basilar skull or cribriform fracture and a cerebrospinal fluid (CSF) leak have greater risk for pneumococcal meningitis, as do children with asplenia (anatomic or functional) or human immunodeficiency virus (HIV) infection. Deficiencies in terminal components of complement lead to greater risk for meningococcal infection. Common causes of meningitis after penetrating head trauma or neurosurgery are staphylococcal species, streptococci, and gram-negative enteric bacilli, especially Escherichia coli, Klebsiella spp., and Pseudomonas aeruginosa. These organisms are also associated with meningitis related to a dermal sinus or embryopathy of the neurenteric canal. Nontypable H. influenzae meningitis is associated with immunoglobulin deficiencies, and Listeria meningitis with cellular immune defects; Listeria meningitis occurs occasionally in immunocompetent infants and children as well. Salmonella spp. rarely cause meningitis in immunocompetent children beyond the neonatal period, and some cases have been linked to reptile pets. The presence of a ventriculoperitoneal shunt is a risk factor for meningitis; ventriculitis related to shunt contamination and skin organisms are usually causative. Isolation of an organism other than pneumococcus, meningococcus, or Hib from the CSF of a child older than 2 months always requires an explanation or evaluation for unusual host susceptibility. Children with recurrent pneumococcal or meningococcal infections also should undergo thorough investigation, including neuroimaging studies.

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