Epidemiology of bacterial meningitis in Niamey, Niger, 1981-96

In the African meningitis belt the importance of endemic meningitis is not as well recognized as that of epidemics of meningococcal meningitis that oc cur from time to time. Using retrospective surveillance, we identified a to tal of 7078 cases of laboratory-diagnosed bacterial meningitis in Niamey, N iger, from 1981 to 1996. The majority (57.7%)were caused by Neisseria menin gitidis, followed by Streptococcus pneumoniae (13.2%) and Haemophilus influ enzae b (Hib) (9.5%). The mean annual incidence of bacterial meningitis was 101 per 100 000 population (70 per 100 000 during 11 non-epidemic years) a nd the average annual mortality rate was 17 deaths per 100 000. Over a 7-ye ar period (including one major epidemic year) for which data were available , S. pneumoniae and Hib together caused more meningitis deaths than N. meni ngitidis. Meningitis cases were more common among males and occurred mostly during the dry season. Serogroup A caused 85.6% of meningococcal meningiti s cases during the period investigated; three-quarters of these occurred am ong children aged <15 years, and over 40% among under-5-year-olds, Both inc idence and mortality rates were highest among infants aged <1 year. In this age group, Hib was the leading cause of bacterial meningitis, followed by S, pneumoniae. The predominant cause of meningitis in persons aged 1-40 yea rs was N. meningitidis. Use of the available vaccines against meningitis du e to N. meningitidis, S. pneumoniae, and Hib could prevent substantial ende mic illness and deaths in sub-Saharan Africa, and potentially prevent recur rent meningococcal epidemics.