associated with the induction of bactericidal activity. Nasopharyngeal colonization with meningococcal strains also results in the induction of bactericidal antibody, although induction of antibody to the capsular polysaccharides is variable. Enteric colonization with organisms of other genera that elaborate the same or similar surface antigens as those of the meningococcus occurs commonly and also probably induces bactericidal antibody. Induction of capsular antibodies early in life is the goal of the current polysaccharide vaccines.
The Sahel region of Africa represents a geographic and epidemiologic special case. The climatically defined area between the 300 mm and 1,100 mm isohyets (lines joining points receiving equal amounts of precipitation over a specified period of time) has been termed the “meningitis belt.” It extends across the Sahel from Ethiopia to eastern Senegal and The Gambia. An extension extends southward through Uganda, Kenya, and Tanzania. All or parts of the following countries are included in the belt: Ethiopia, Sudan, Central African Republic, Chad, Niger, Nigeria, Cameroon, Benin, Ghana, Ivory Coast, Burkina Faso (formerly Upper Volta), Mali, Guinea, Senegal, The Gambia, and Mauritania. In this belt, massive epidemics of group A meningococcal disease occur about every 10 years. Because of the devastating nature of these predictable epidemics, global strategies for preventing meningococcal disease must be targeted to this area to be successful.
Meningococcal disease is seasonal. Survival of the meningococcus in aerosolized droplets is highly dependent on humidity, but not temperature. Humidity conditions favorable to transmission of the meningococcus can occur in temperate climes in late winter and early spring, and with the transition from dry to wet seasons in South America and sub-Saharan Africa. During these times the incidence of endemic disease increases and epidemics occur.
Epidemics have also occurred in recent years in southwest Asia, Nepal, India, China, Brazil, and Finland. Epidemic meningococcal disease does not occur in deserts or in invariably humid climates, such as in rain forests or deserts. Endemic meningococcal disease is presumed to be distributed worldwide, although data are not available from most areas.
Little reliable data are available on the worldwide incidence of meningococcal meningitis from which to estimate the disease burden arising from endemic and epidemic disease caused by N. meningitidis. The following calculations have been extrapolated from those studies that have been published and rely, of necessity, on informed judgment.