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. Serogroup B, generally associated with sporadic disease, may cause some upsurges or outbreaks. Transmission is by direct contact, including respiratory droplets from nose and throat of infected persons.
Most infections are subclinical and many infected people become symptomless carriers.
Waning immunity among the population against a particular strain favours epidemics, as do overcrowding and climatic conditions such as dry season or prolonged drought and dust storms. Upper respiratory tract infections may also contribute to the development of epidemics. Infants may have illness without sudden onset and stiff neck. Laboratory examination of the cerebrospinal fluid will usually confirm the presence of a bacterial meningitis. More specialized laboratory tests, which may include culture of cerebrospinal fluid and blood specimens, are needed for identification of Neisseria meningitidis and the serogroup as well as its susceptibility to antibiotics.