A different pattern, with epidemics flaring for two to three consecutive years, has been observed in countries in sub-Saharan Africa. This area has experienced epidemic cycles every eight to 12 years in the past, and the intervals between major epidemics have become shorter and more irregular since the beginning of the 1980s. The most recent meningococcal meningitis pandemic, which began in 1996, has so far resulted in approximately 300,000 cases being reported to the World Health Organization. The most affected countries have been Nigeria, Burkina Faso, Mali and Niger. Approximately 500,000 of these cases and 50,000 of the deaths are due to meningococcus.
Meningococcal meningitis is the only form of bacterial meningitis which causes epidemics.
Epidemics occur in the dry season in this area. While the highest disease rates are found in young children, during epidemics older children, teenagers and young adults are also affected. A large widespread epidemic can follow on from a localised outbreak the previous year and incidence rates remain elevated during the following 1-2 years unless the appropriate control measures including mass immunisation are instituted. Neisseria meningitidis , a Gram-negative bacterium. Serogroup A and C meningococci are the main causes of epidemic meningitis.