Epidemiology of Meningitis and Ventriculitis in Children

Incidence and Prevalence

Bacterial meningitis

• 25,000 – 40,000 cases per year: The number of bacterial meningitis cases in the United States is estimated at 25,000 – 40,000 cases per year, with most cases occurring in children younger than 5 years of age.
• 25 – 100 per 100,000 live births: Bacterial meningitis is most common in the first month of life, with an incidence of 0.25 to 1 per 1000 live births (6, 32).
• 17 per 100,000 incidence of pneumococcal meningitis: The average incidence of pneumococcal meningitis worldwide is 17 cases per 100,000, varying from 6 cases per 100,000 in Europe to 38 cases per 100,000 in Africa (48).
• 31 per 100,000 incidence of H. influenzae type b meningitis: The average worldwide incidence for H. influenzae type b meningitis is 31 cases per 100,000, varying from 13 cases per 100,000 in Europe to 46 cases per 100,000 (72).

Tuberculous meningitis

• Prevalence of TB meningitis 2.1 per million: Globally, there were an estimated 13.7 million cases of TB in 2007 (206 per 100 million) (29).
• Globally, TB meningitis accounts for 7% of hospital admissions: It may account for up to 7% of all admissions to pediatric specialty hospitals in certain developing countries (67, 29).

Viral meningitis

• 10,000 cases per year in United States: More than 10,000 cases of viral meningitis are reported annually in the United States, but the actual number may be closer to 75,000, as many cases are not reported due to the indolent nature of the illness and the difficulty in identifying a viral cause.
• 11 cases per 100,000 per year incidence in United States: An annual incidence of 11 cases per 100,000 population per year has been reported by the CDC. Worldwide estimates are even more difficult to come by, due to the clinically heterogeneous and benign nature of these illnesses, but one study from Greece reported an incidence of 14 cases per 100,000 children under the age of 14 per year (47).

Fungal meningitis

• 50 to 270 per 100,000 Candida albicans meningitis in infants: Candida albicans infection resulting from indwelling catheters or secondary colonization during antibiotic therapy for bacterial infections may occur in the relatively immunocompromised infant (26). The annual incidences of candidemia per 1000 patient-days for infants varies on the basis of birth weight, from 0.5 for infants weighing more than 2500 g to 2.68 for infants weighing less than 1000 g. The overall incidence of systemic C. albicans infection in infants under 1000 g is 5.1 percent (27). C. albicans meningitis may develop in 25% of patients with systemic C. albicans infection.
• Candida most common fungal meningitis in immunocompromised patients: Patients with immunodeficiency secondary to chemotherapy, bone marrow or solid organ transplantation, or acquired immunodeficiency syndrome (AIDS) may develop fungal meningitis most commonly due to either C. albicans or Aspergillus fumigatus. The incidence of candidemia varies widely among populations, between 1.9 and 10 per 100,000 children in various reports (15). A small proportion of these children may develop Candida meningitis.
• 2.79% prevalence of cryptococcal meningitis in HIV: Cryptococcal meningitis is one of the presenting manifestations of AIDS and is the most common lethal fungal infection in patients with AIDS worldwide (5). In one study of 573 HIV seropositive patients, the prevalence of cryptococcal meningitis was 2.79% (5).

Age Distribution

Bacterial meningitis

• Infancy – H. influenzae: H. influenzae type b meningitis is primarily a disease of infancy. The incidence peaks in the first year of life, with most cases occurring between 3 months and 3 years of age. Before age 3 months most infants are protected by passively acquired maternal antibodies. Children naturally develop immunity to H. influenzae after the age of 3 years, and serum antibody concentrations reach adult levels by 7 years of age (17).
• Peak in infancy – meningococcal and pneumococcal: Meningococcal and pneumococcal meningitis are most common in the first year of life, rarely occurring in infants younger than 3 months of age. Unlike H. influenzae, these two pathogens may cause systemic infections at any age in both children and adults.
• Infants and young children: Pneumococcal meningitis is slightly more common than meningococcal meningitis.
• Children older than 5 years: N. meningitidis (meningococcal meningitis) accounts for 59% cases of meningitis in older children.

Tuberculous meningitis

• Highest risk in infancy: The natural history and clinical presentation of tuberculosis are different in children than in adults, with neonates having the highest risk of progression to severe forms of TB.

Viral meningitis

• Young age: Enterovirus meningitis, the most common viral meningitis, is more prevalent among younger children.

Fungal meningitis

• Young age: Candida infections appear in neonates, especially those weighing less than 1000 g. In older patients, these infections are typically associated with immunosuppression due to organ or stem cell transplants or HIV.

Sex Predilection

• Bacterial meningitis: More common in males.
• Viral meningitis: Varies with viral pathogen. The enterovirus M:F ratio is 1.3–1.5, while the mumps M:F ratio is about 3.
• Fungal meningitis: More common in males, particularly in patients with HIV.

Geographic Distribution

Bacterial meningitis

• Gram-negative enteric bacilli meningitis in the emerging world: In developing countries, gram-negative enteric bacilli are the most common organisms causing neonatal bacterial meningitis (28). While the incidence of Salmonella meningitis is only 1% in the United States, in developing countries it may account for 5–13% of acute bacterial meningitis cases (74), with high morbidity and mortality.

Tuberculous meningitis

• Dense populations and Africa: The countries with the highest number of TB cases are India, China, Indonesia, Nigeria, and South Africa (29).

Viral meningitis

• Regions not protected with vaccines: Epidemics occur in summer and fall. Mumps is responsible for 10–20% of cases of viral meningitis in areas where vaccines are not available.

Fungal meningitis

• Regional variation in species: The causes of community-acquired fungal meningitis vary regionally, and are represented by Coccidioides immitis in the southwestern United States and Mexico, Cryptococcus neoformans (by far the most common world-wide), Histoplasma capsulatum in the midwestern United States, and Blastomyces dermatitidis in the southern United States (14, 68).

Risk Factors

Bacterial meningitis

• Neonatal bacteremia, preterm birth, or complicated delivery: Acute bacterial meningitis occurs in about 25% of cases of neonatal bacteremia (38). Risk factors for bacterial meningitis include preterm birth, prolonged rupture of fetal membranes, maternal chorioamnionitis, and the presence of group B β-hemolytic streptococci (GBS), gram-negative enteric bacteria, and Listeria monocytogenes.
• Prolonged intensive support of neonate: In neonates requiring prolonged hospitalization with central venous catheters, parenteral nutrition, and ventilator support, meningitis due to coagulase-negative Staphylococcus species or Pseudomonas species may be seen (50).
• Maternal listeriosis: L. monocytogenes is usually associated with maternal infection and acquired from contaminated milk products.
• Genetic factors: There is an extremely high incidence of bacterial meningitis among American Indians and Alaskan Eskimos, suggesting that genetic factors may play a role in the development of meningitis.
• Overcrowded living conditions: Environmental factors, including overcrowded living conditions, have been shown to increase the risk of airborne transmission of bacteria and have led to secondary infections and epidemics. Although racial differences in the incidence of bacterial meningitis have been reported, it appears that the increased incidence of meningitis among blacks and Hispanics in developed countries may be accounted for by socioeconomic factors, rather than genetic factors.
• Immunodeficiency: Other risk factors include congenital or acquired immunodeficiency syndromes, including IgG or complement deficiencies, or absence or altered function of the spleen. In Africa, sickle cell disease has been associated with a marked increase in the risk of infection by invasive bacteria, such as S. pneumoniae (36-fold increase) and H. influenzae type b (13-fold increase) (54).
• Congenital or acquired CSF tracks: Patients with neurocutaneous tracts or fistulas, CSF leaks (either traumatic or postoperative), or severe ear or sinus infections have also been shown to have an increased risk of bacterial meningitis (79).
• CSF shunt: The presence of a neurosurgical cerebrospinal fluid shunt or reservoir is a risk factor for meningitis (38).

Tuberculous meningitis

• Overcrowding and other socioeconomic factors: Predisposing factors for tuberculous meningitis include poverty, overcrowding, illiteracy, and malnutrition (29).
• Immunocompromised patients: Diabetes mellitus, immunosuppression, and HIV infection increase the risk for becoming infected with TB (29).
• Substance abuse: Alcoholism and substance abuse are risk factors for contracting TB (29).
• Other: Malignancy and head trauma have been associated with an increased risk for TB (29).

Viral meningitis

• Summer and fall temperate climates: Most viral infections occur in the summer and fall in temperate climates, but they may occur year round in more tropical climates.
• Socioeconomic factors and immunocompromised patients: Viral meningitis is more prevalent in lower socioeconomic groups and in immunocompromised hosts.

Fungal meningitis

• Immunocompromised patients: Fungal meningitis is most commonly seen in immunocompromised patients. 25% of neonates with systemic C. albicans may develop fungal meningitis when being treated for severe bacterial infections due to their relatively immunocompromised state, due to the need for indwelling catheters or from secondary colonization during antibiotic therapy for bacterial infections (26). Patients with immunodeficiency secondary to chemotherapy, bone marrow or solid organ transplantation, or due to AIDS may develop fungal meningitis, most commonly due to either C. albicans or A. fumigates.

Relationships to Other Disease States and Syndromes

Bacterial meningitis

• Systemic bacterial infections and trauma: Bacterial meningitis may be associated with sepsis, sinus infections, otitis media, penetrating trauma, or neurosurgical procedures.

Tuberculous meningitis

• Increased incidence in HIV patients: The incidence of TB meningitis varies with HIV status, being 2% in patients without HIV and 14% in HIV-infected patients (29). In patients with HIV infection, there may be up to 50% incidence of extrapulmonary involvement, including increased risk of TB meningitis (9, 57).

Viral meningitis

• Impaired access to health care: Viral meningitis is commonly associated with lower socioeconomic groups, crowded living conditions, and immunocompromised individuals.

Fungal meningitis

• Immunocompromised patients: Fungal meningitis is most commonly seen in immunocompromised patients. 25% of neonates with systemic C. albicans may develop fungal meningitis when being treated for severe bacterial infections due to their relatively immunocompromised state, due to the need for indwelling catheters or from secondary colonization during antibiotic therapy for bacterial infections (26). Patients with immunodeficiency secondary to chemotherapy, bone marrow or solid organ transplantation, or due to AIDS may develop fungal meningitis, most commonly due to either C. albicans or A. fumigates.