Bugs – MENINGOCOCCAL MENINGITIS
Meningococcal meningitis is the only form of bacterial meningitis which causes epidemics. Epidemics occur in the winter-spring period in temperate zones and in the dry season in tropical countries. The highest rates occur in young children, while during epidemics older children, teenagers and young adults are also affected.
Mode of Infection
Meningococcal meningitis is a disease caused by the 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, as in Cuba (1982-1984) Chile (1986, 1993) and Brazil (1988).
Meningococcal meningitis has an incubation period of 2- l0 days, (often 3-4 days) and is characterized by sudden onset of intense headache, fever, nausea, vomiting, photophobia, and stiff neck. Neurological signs include lethargy, delirium, coma and/or convulsions. Infants may have illness without sudden onset and stiff neck. Case fatality rate is between 5% and 15% if diagnosed early and 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.
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.
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 and Nepal in the mid-l980s and Mongolia in 1994-1995.
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 disease is potentially fatal and 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. However, isolation of the patient is not necessary. A range of drugs may be used depending on antibiotic susceptibility. Oily chloramphenicol may be the drug of choice in areas with limited health facilities because a single dose of the long-acting form has been shown to be effective (in field conditions in Africa).
Epidemics usually spread rapidly to a peak within weeks but may last for several months in the absence of vaccination. A mass vaccination campaign can halt an epidemic due to serogroups A or C, ldeally, mass vaccination of the entire population should be considered but when resources are limited, vaccination may be restricted to the groups most at risk such as those with the highest attack rates or accounting for the largest proportion of cases.
Travellers to areas affected by meningococcal outbreaks should be vaccinated. Vaccines are available against serogroups A, C, W 135 and Y (quadrivalent).