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RAPID HEALTH ASSESSMENT PROTOCOLS FOR EMERGENCIES
( By WHO - OMS, 1999 )

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3 - Background

Geographical distribution

Meningococcal meningitis, caused by the organism Neisseria meningitidis, is responsible for epidemic emergencies that are particularly severe in sub-Saharan Africa. In areas within the “meningitis belt”, epidemics occur in 8 to 12 year cycles and are characterized by attack rates as high as 1%, mortality rates of up to 10%, even with treatment, and neurological sequelae among survivors.

However, outbreaks of meningococcal disease have reached other African countries. The epidemics seen towards the end of the 1980s and the early 1990s in Burundi, the Central African Republic, Kenya, Rwanda, Uganda, the United Republic of Tanzania and Zambia are examples of the disease’s spread outside its usual boundaries. This reflected the extension of drought areas, or increased population movements owing to voluntary travel, warfare or movements of refugees. The outbreaks may also reflect the introduction of a new meningococcal strain into susceptible populations.

Cluster outbreaks in the Eastern Mediterranean Region have also occurred through transmission at international gatherings, such as pilgrimages. At a country level, epidemics have been reported in at-risk settings such as refugee camps, military facilities, and disadvantaged communities. The risk of person-to-person transmission is greatly increased in these populations since the disease is spread through respiratory droplets from cases with nasopharyngitis or from asymptomatic carriers.

Recently, Mongolia has experienced epidemics of magnitude comparable to that of the meningitis belt. India and Nepal also had serious outbreaks in the mid-1990s.

Epidemic threshold

For countries with high rates of endemic meningitis, such as those within the traditional meningitis belt, a rate of 15 cases per 100 000 per week in a given area, averaged over two consecutive weeks, appears to be a sensitive and specific predictor of epidemic disease in this area.

In areas where epidemic meningococcal disease is unusual, a three- to four-fold increase in cases compared with a similar time period in previous years may indicate an epidemic. Another potentially useful indicator of an emerging epidemic in areas outside the meningitis belt is a doubling of meningitis cases from one week to the next for a period of three weeks. This criterion may be used, for example, in countries where population data are not available, in refugee camps, and in closed communities.

Vaccines

Vaccines are currently available to prevent meningococcal meningitis caused by serogroups A, C, Y and W135, usually provided as bivalent A and C, or quadrivalent vaccines.

A single dose of group A vaccine protects those over one to two years of age. Data show that antibody levels rise within 7 to 10 days of vaccination. Children of three months to two years of age may benefit from a second dose, although the vaccine’s efficacy has not been proven for this age group. The duration of protection in adults is at least three years.

Group C vaccine has not been shown to be effective in children under two years old.

Treatment

A single intramuscular injection of long-acting chloramphenicol in oil has been proved effective in meningococcal meningitis epidemics. If there is no clinical improvement after 24 to 48 hours, a second dose should be given. Penicillin, ampicillin, and chloramphenicol are also effective, but require multiple doses and, in severe cases, intravenous administration.

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