Meningococcal meningitis occurs globally. It shows an endemic pattern in temperate climates, causing a steady number of sporadic cases or small clusters with seasonal increase in the winter period. Some endemic countries have reported an increasing annual number of cases over the last decade. A different pattern, with epidemics recurring during 2-3 consecutive years has been observed in other parts of the world. Transmission is by direct contact, including respiratory droplets from nose and throat of infected persons.
Most infections are subclinical, and many infected become symptomless carriers.
Waning immunity among the population against a particular strain favours epidemics, as do overcrowding, climatic conditions such as dry season or prolonged drought and dust storms. Upper respiratory tract infections may also contribute to the development of epidemics. Meningococcal meningitis is characterized by sudden onset of intense headache, fever, nausea, vomiting, photophobia, and stiff neck. Infants may have illness without sudden onset and stiff neck. Travellers to areas affected by meningococcal outbreaks should be vaccinated.