Meningococcal meningitis is caused by the bacterium, Neisseria mengititis: 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. Countries in sub-Sahara Africa have experienced large outbreaks every 8-12 years in the past, but intervals between major epidemics have become shorter & more irregular since the beginning of the 1980s.
Epidemiology: Meningococcal meningitis is the only form of bacterial meningitis which causes epidemics. The largest epidemics of meningococcal meningitis have been reported in sub-Saharan African countries within the meningitis belt (which extends from Ethiopia in the east to Senegal in the west, mainly within the range of 300 mm annual rainfall) but epidemic meningococcal disease can occur in any country regardless of climate. For example, India & Nepal in the mid-1980s & Mongolia in 1994-1995. Epidemics occur in the winter-spring period in temperate zones & in the dry season in tropical countries. The highest rates occur in young children, while during epidemics older children, teenagers & young adults are also affected.
A large widespread epidemic can follow the local outbreak during the second year of the cycle (and incidence rates reman elevated during the following 1-2 years with successive seasonal outbreaks separated by remissions).
Etiological agent: Meningococcal meningitis is a disease caused by the Neisseria meningitidis, a Gram-negative bacterium. Serogroup A & C meningococci are the main causes of epidemic meningitis, but serogroup W & Y have been associated with travel related transmission. Serogroup B, generally associated with sporadic disease, may cause some upsurges or outbreaks, as in Cuba (1982-1984) Chile (1986, 1993) & Brazil (1988) .
Transmission: Transmission is by direct contact, including respiratory droplets from nose & throat of infected persons. Most infections are subclinical, & 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 & dust storms. Upper respiratory tract infections may also contribute to the development of epidemics.
Incubation period: 2-10 days, often 3-4 days
Clinical picture: Meningococcal meningitis is characterized by sudden onset of intense headache, fever, nausea, vomiting, photophobia, & stiff neck. Neurological signs include lethargy, delirium, coma and/or convulsions. Infants may have illness without sudden onset & stiff neck. Case fatality rate is between 5% & 15% if diagnosed early & given adequate therapy but may exceed 50% in the absence of treatment. A less common but more severe (often fatal) form of meningococcal disease is meningococcal septicaemia.
Diagnosis: Specialized laboratory tests of cerebrospinal fluid & blood specimens followed for identification of Neisseria meningitidis & the serogroup as well as its susceptibility to antibiotics.
Therapy: Meningococcal disease is potentially fatal & should always be viewed as a medical emergency. Admission to a hospital or health centre is necessary. Antimicrobial therapy must be instituted as soon as possible after the lumbar puncture has been carried out.
Chemoprophylaxis: Can be considered for people in close contact with patients in the endemic situation. It is not an effective means of interrupting transmission during an epidemic. Potential antimicrobials for chemoprophylaxis are rifampicin, mynocycline, spiramycin, ciprofloxacin & ceftriaxone. Sulfonamides are only useful when circulating meningococci are identified as susceptible.
Vaccination: Travellers to areas affected by meningococcal outbreaks should be vaccinated. Vaccine protects against serogroups A, C, W 135 & Y (quadrivalent), & protection lasts for about 2-3 years.