The epidemiology of viral meningitis hospitalization in childhood.

BACKGROUND: There have been few long-term population-based studies of viral meningitis, and only a limited number of potential risk factors have been evaluated.
METHODS: We estimated the incidence of viral meningitis hospitalization in childhood, and assessed risk factors for this disease through a population-based cohort study comprising all children born in Denmark from 1977 through 2001 (n = 1.5 million). Information on sex, number of children and adults in the household, age of parents at child's birth, degree of urbanization, birth weight, gestational age, and possible complications at birth were linked to the children in the cohort, together with information on hospitalization with viral meningitis. We calculated incidence rates of viral meningitis and estimated rate ratios according to the various risk factors using Poisson regression.
RESULTS: The incidence rate was highest in the first 6 months of life (38.7 per 100,000 person-years), with a peak right after birth (58.7 per 100,000 person-years). A secondary peak was seen among 5-year-old children (15.6 per 100,000 person-years). Overall incidence rates decreased throughout the study period, with outbreaks occurring every 3 to 5 years [decrease in rate ratio per calendar year = 0.95; 95% confidence interval (CI) = 0.94-0.96]. Summer and early fall peaks were present. We observed independent effects of sex (girls vs. boys: rate ratio = 0.47 [95% CI = 0.43-0.53]), children in the household (eg, living with 3+ younger children vs. living with none: 1.94 [1.22-3.07]), single parenthood (living with 1 parent vs. living with 2 parents: 1.30 [1.12-1.39]), degree of urbanization (children living in the capital vs. children living in small town and rural areas: 1.54 [1.31-1.80]), low birth weight (increase in RR per 500 g reduction in birth weight = 1.05 [1.00-1.09]), prematurity (increase in RR per 1 week reduction in gestational age = 1.03 [1.01-1.04]), and cesarean section (cesarean section vs. vaginal birth: 1.29 [1.12-1.49]).
CONCLUSIONS: Incidence of viral meningitis hospitalization is highest immediately after birth with a secondary peak at age 5. Lack of passive maternally acquired antibodies and preferential hospitalization are the likely causes for the peak in infancy. Increased transmission in kindergarten, preschool, and day care could explain the secondary peak. The incidence decreased throughout the 25-year study period perhaps due to improved public hygiene. Among the assessed risk factors, we found the strongest to be male sex, a high number of children in the household, and degree of urbanization.