Epidemics of meningitis occur worldwide. However,
the “meningitis belt” of Africa’s Sahel region has the
greatest incidence of the disease, with large epidemics
attributed to predominantly group A meningococci; the
endemic levels found in this region would be considered
epidemic elsewhere. Although factors predisposing populations
to meningitis epidemics are poorly understood,
population susceptibility, introduction of new strains, poor
living conditions, and concurrent infections have all been
implicated. Epidemics occur throughout Africa in the dry
season, coincide with periods of very low humidity and
dusty conditions, and disappear with the onset of the rains,
suggesting that these environmental factors may also play
an important role in the occurrence of the disease (1–3).
Lapeyssonnie (4) observed in 1963 that epidemics
largely occurred in a semi-arid zone south from the Sahara,
with 300–1,100 mm mean annual rainfall, and Cheesbrough
et al. (5) suggested in 1995 that areas that are
humid throughout the year have low disease rates. In West
Africa, Waddy (1958) described an area that suffered epidemics
as having “…only one definable frontier, the junction
of the forest…with the savanna…, when there is an
abrupt change from a permanently humid climate to one
with a severe dry season” (6). Epidemics have been rarely
reported from the humid forested or coastal regions, even
when neighboring areas are severely affected