The bacterium Neisseria meningitidis. Most cases of meningococcal disease are caused by serogroups A, B and C; less commonly, infection is caused by serogroups Y (emerging in the United States) and W-135 (particularly in Saudi Arabia and west Africa) and rarely by serogroup X (Africa, Europe, United States).
Transmission occurs by direct person-to-person contact and through respiratory droplets from the nose and pharynx of infected individuals, patients or asymptomatic carriers. Humans are the only reservoir.
Nature of the disease
Most infections do not cause clinical disease. Many infected people become asymptomatic carriers of the bacteria and serve as a reservoir and source of infection for others. In general, susceptibility to meningococcal disease decreases with age, although there is a small increase in risk in adolescents and young adults. Meningococcal meningitis has a sudden onset of intense headache, fever, nausea, vomiting, photophobia and stiff neck, plus various neurological signs. The disease is fatal in 5–10% of cases even with prompt antimicrobial treatment in good health care facilities; among individuals who survive, up to 20% have permanent neurological sequelae. Meningococcal septicaemia, in which there is rapid dissemination of bacteria in the bloodstream, is a less common form of meningococcal disease, characterized by circulatory collapse, haemorrhagic skin rash and high fatality rate.
Sporadic cases are found worldwide. In temperate zones, most cases occur in the winter months. Localized outbreaks occur in enclosed crowded spaces (e.g. dormitories, military barracks). In sub-Saharan Africa, in a zone stretching across the continent from Senegal to Ethiopia (the African “meningitis belt”), large outbreaks and epidemics take place during the dry season (November to June). Recent reports of group Y meningococcal disease in the United States, and outbreaks caused by serogroup W-135 strains in Saudi Arabia and sub-Saharan Africa, particularly Burkina Faso, suggest that these serogroups may be gaining in importance.
Risk for travellers
The risk of meningococcal disease in travellers is generally low. Those travelling to industrialized countries may be exposed to sporadic cases mostly of A, B or C. Outbreaks of meningococcal C disease occur in schools, colleges, military barracks and other places where large numbers of adolescents and young adults congregate.
Travellers to the sub-Saharan meningitis belt may be exposed to outbreaks, most commonly of serogroup A and serogroup W135 disease, with comparatively very high incidence rates during the dry season (December to June). Long-term travellers living in close contact with the indigenous population may be at greater risk of infection.
Pilgrims to Mecca are at particular risk. The tetravalent vaccine, (A, C, Y, W-135) is currently required by Saudi Arabia for pilgrims visiting Mecca for the Hajj (annual pilgrimage) or for the Umrah.
Avoid overcrowding in confined spaces. Following close contact with an individual suffering from meningococcal disease, medical advice should be sought regarding possible chemoprophylaxis.