Essential facts about the meningococcus

1.        Meningococcal disease is a growing problem worldwide, especially in sub-Saharan Africa.

2.        The highest burden of meningococcal disease occurs in the African Meningitis Belt, which extends from Senegal to Ethiopia. The region  is home to about 500 million people who are at risk of contracting the disease.

3.        Meningococcus serogroup A causes more than four-fifths of meningitis cases in the African Meningitis Belt

4.        Immunity to meningococcal disease is serogroup-specific.

5.        Most serogroups causing meningococcal disease are VACCINE PREVENTABLE.

6.        Meningococcal polysaccharide vaccines are safe and effective in persons two years of age and older, but the immunity they induce wanes over time.

7.        Meningococcal conjugate vaccines are safe and effective in young infants and adults alike and produce long lasting immunity.

8.        Ministers of Health from countries of the African Meningitis Belt committed themselves in the Yaoundé Declaration of 2008 to introduce the meningococcal A conjugate vaccine (MenAfriVac) into their national immunisation programmes. Their aim is to eliminate periodic epidemics of meningococcal group A meningitis in the region.

9.        People at risk of vaccine-preventable meningococcal disease should receive meningococcal vaccination.

10.    Early identification of severe meningococcal disease and institution of appropriate antibiotics will prevent death. 

What is meningococcal disease?

Meningococcal disease is a severe acute bacterial infection caused by Neisseria meningitidis (the meningococcus). It can take the form of meningitis, septicaemia, or focal infections. Meningitis is an infection of the meninges, the thin lining that surrounds the brain and the spinal cord.  Several different bacteria can cause meningitis. The meningococcus is one of the most important causes because of its potential to cause epidemics. Meningococcal septicaemia (or meningococcaemia) refers to blood stream infection by the meningococcus.

The pathogen

The meningococcus is an aerobic, Gram-negative, encapsulated bacterium commonly occurring in pairs (diplococci). At least 13 serogroups have been identified, based on characteristics of the polysaccharide capsule. Most invasive disease is caused by serogroups A, B, C, Y, and W-135. Relative importance of serogroups depends on geographic location and other factors such as age. Differences in the outer membrane proteins are used to further distinguish different serotypes and subtypes. The polysaccharide capsule and the lipopolysaccharide component (endotoxin) of the bacterial cell wall are important virulence factors. Serogroups determine the pathogenicity, immunogenicity, and epidemic potential of the meningococcus. Thus the identification of the serogroup responsible for a sporadic case is crucial for epidemic containment.

Clinical picture of meningococcal disease

The most common symptoms of meningitis are high fever, headache, stiff neck, sensitivity to light, confusion, and vomiting. Meningococcaemia may occur with or without meningitis. It is characterised by fever, petechial or purpuric rash, hypotension, and multiple organ failure.  Meningococcal disease rarely presents as pneumonia, endolphthalmitis, or chronic meningococaemia. 

Meningococcal disease is associated with high case-fatality rates (5-25%) even where adequate medical services are available. In Cape Town, 10-30% of survivors develop sequelae such as neurological disability, deafness, skin scarring, and amputations.

The epidemiology of meningococcal disease 

How is meningococcal disease spread?

The bacteria are transmitted from person to person through droplets of respiratory or throat secretions. Close and prolonged contact such as kissing, sneezing and coughing on someone, and overcrowding (crèches, colleges, military, etc) facilitate transmission of the bacteria. The meningococcus only infects humans. It is estimated that 10-25% of the population carries N. meningitidis in the pharynx at any given time, but the carriage rate is much higher in epidemic situations.

What are the risk factors for meningococcal disease?

Risk factors for meningococcal disease are linked to exposure and or host factors. Exposure factors include household exposure, overcrowding (military and police recruits, refugees and young people who live in dormitories such as college and first year university students), and smoking. Host factors include age (children under five years of age and young adults are at highest risk), terminal complement component deficiency, and asplenia.

What is the incubation period for meningococcal disease?

The average incubation period for meningococcal disease is 4 days (range 2-10 days).

What is the incidence of meningococcal disease?

The average incidence rates of meningococcal disease are 0.5-5 cases per 100,000 people per year in high-income countries, 5-50 cases per 100,000 people per year in low and middle-income countries. In South Africa, the incidence rate is of the order 3-6 cases per 100,000 people per year. The rates increase dramatically during epidemics.

In general, meningococcal disease occurs sporadically in small clusters throughout the world, with seasonal variations, and accounts for a variable proportion of endemic bacterial meningitis. In temperate regions the number of cases increases in winter and spring. Serogroups B and C together account for a large majority of cases in Europe and the Americas. Several outbreaks due to meningococcal serogroup C were reported in North America between 1992 and 1997.

The most prominent meningococcal serogroups are A, B, C, Y, and W135. While groups A, B, and C are responsible for the majority of cases worldwide, group A causes periodic deadly, explosive epidemics in a well-defined geographical area in sub-Saharan Africa known as the “African Meningitis Belt”. Outside Africa, only Mongolia reported a large epidemic in recent years (1994-95). There is some evidence of serogroup W135 increasingly associated with outbreaks of considerable size. In 2000 and 2001 several hundred pilgrims attending the Hajj in Saudia Arabia were infected with meningococcus group W135. Then in 2002, the serogroup caused a major epidemic in Burkina Faso.

In South Africa, serogroup B predominates in the Western Cape Province and other serogroups predominate in the provinces of the country. In 2008, a total number of 456 meningococcal disease cases were reported from all provinces in the country. The majority of these cases were reported from Gauteng Province (224 of 456, 49%). In this province, the predominant serogroup was W135 (103 [64%] of 162 cases with viable bacterial isolates available for serogrouping). The other prevalent meningococcal serogroups in the province were serogroups B (n=28) and C (n=21).

The African Meningitis Belt

The highest burden of meningococcal disease in the world occurs in the African Meningitis Belt, which stretches from Ethiopia in the east to Senegal and Gambia in the west. The reasons for the onset of epidemics in this region are not completely understood. However, disease transmission occurs during the dry season which occurs between December and June, characterised by dusty dry winds and cold nights. Other factors that may favour transmission of the meningococcus include poor living conditions and overcrowded housing, travel and large population movements, and drought.

Epidemic meningitis has been present on the African continent for about a century. Large epidemics usually take place in irregular cycles every 5-10 years. Serogroups A, C and W135 are now the main serogroups involved in meningococcal meningitis epidemics in Africa; with group A meningococci accounting for four-fifths of all cases. The size of the epidemics can be enormous. In 1996, Africa experienced the largest recorded outbreak of epidemic meningitis in history, with over 250,000 cases and 25,000 deaths reported. Though Africa has been relatively spared in recent years, during the first 11 weeks of 2009 (i.e. 1 January to 15 March) a total of 24,868 suspected cases of meningitis (including 1,513 deaths) were reported by countries of the African Meningitis Belt. These cases were characterised by the predominance of serogroup A and more than 85% occurred in one epidemic focus around northern Nigeria and Niger. About 500 million people living in countries of the meningitis belt are at risk of contracting the meningococcus.