Trends of etiology of acute bacterial meningitis in Chilean children from 1989 to 1998. Impact of the anti-H influenzae type b vaccine

Acute bacterial meningitis still has a high mortality and rate of complications. To assess the impact of anti H influenzae vaccination on the epidemiology of acute bacterial meningitis in Chilean children. A retrospective study of hospital discharge records of patients with acute bacterial meningitis. Causative agents were studied globally, by hospital and by age group. The changes in etiology from 1989 to 1995 were also assessed. Between 1996 and 1998, only those patients with acute bacterial meningitis caused by H influenzae were recollected. In the period prior to vaccination (1989-1995), 1000 cases were registered. The main causative agents were N meningitidis in 33.8%, H influenzae type b in 21.9% and S pneumoniae in 15.4%. The incidence of H influenzae decreased in the period from 36.4 to 9.9% (p < 0.001) and the incidence of N meningitidis increased from 22.9 to 52.1% (p < 0.001). The incidence of S pneumoniae did not change significantly. H influenzae predominated in children between 4 and 24 months of age and N meningitidis predominated in children over 25 months of age. In the period after the introduction of vaccination (1995-1998), there was a further decrease in the incidence of H influenzae from 10 to 2% (p < 0.001). Until 1997, there was a considerable increase in the incidence of N meningitidis, specially in children over 25 months of age. It declined in 1998 to 38%. There was a reduction in the incidence of acute bacterial meningitis caused by H influenzae prior to the introduction of the vaccine against H influenzae type b. The decrease was more pronounced after the introduction of the vaccine.