Meningitis definition and treatment

Meningitis is an infection of the meninges, which is the membrane that covers the brain and spinal cord like a sheath. It can be caused by a variety of germs, both viral and bacterial. The most dangerous form, however, is caused by the bacterium Neisseria meningitidis, commonly called the meningococcus. This germ is serious both because it is highly virulent for the individuals it affects and because unlike most other causes of meningitis it has the potential to cause epidemics. Meningococcal meningitis occurs in two distinct patterns, endemic and epidemic. In most countries of the world there are sporadic cases from time to time, which means that the meningococcus germ is endemic there at low levels. However there is an area that spans sub-Saharan Africa called the meningitis belt where large epidemics occur regularly, affecting many thousands of people. Such an occurrence usually requires the intervention of specialised teams such as those of MSF. How meningitis kills The meningococcus resides in the nose or throat of health carriers - people who do not themselves fall sick because they have a measure of natural or acquired immunity. They can however spread it to others, and this tends classically to occur during the dry season, from December to February in much of the meningitis belt. If the meningococcus falls upon a susceptible (non-immune) person, it can invade the tissues of the nose and throat. It then multiplies rapidly and spreads into the blood stream and up to the brain, where it has a special affinity for the meninges. The normally clear fluid that surrounds the brain quickly becomes cloudy and more viscous, increasing the pressure within the skull. Meningococci within the bloodstream have their own toxic effect, causing shock (a potentially fatal drop in blood pressure) and bleeding into the skin, which gives rise to the characteristic rash. The case fatality rate for untreated meningococcal meningitis approaches 50 per cent, and even those people who survive may have subsequent brain damage causing disabilities such as paralysis or deafness. Even when it treated early and appropriately, meningitis is an extremely dangerous disease and the patient cannot always be saved - the case fatality rate tends to be between five per cent and 15 per cent. Managing the epidemic In the early stages of a meningitis outbreak it can be difficult for MSF teams in the field to know whether they are dealing with a cluster of sporadic cases or a the start of a true epidemic. The distinction is important, because if an epidemic is coming we need to launch an immediate vaccination campaign, and this has enormous logistic implications - vaccines must be procured from suppliers, the cold chain must be set up, and extra emergency field volunteers must be deployed. MSF therefore uses an arbitrary threshold to decide on when to intervene - an epidemic of meningitis is defined as more than 15 cases per week per 100,000 head of population, over a period of two consecutive weeks. The mainstays of management of an outbreak are:
  • Vaccination. The target group is all persons in the affected region aged two years (or sometimes, as low as three months) to 25 years. Older persons have generally already been exposed to the meningococcus in the past and so have naturally acquired immunity, and they tend thus not to fall sick during an outbreak. Infants do not tend to mount a good immune response to the vaccine, but if the older children and other people in their entourage are all vaccinated this will afford the youngest ones some measure of protection through what is called "herd immunity".
  • Treatment. The antibiotic used by MSF is an oily suspension of chloramphenicol, which is an antibiotic that had largely gone out of favour until applied to this particular use. Suspension in an oily base gives the drug a long duration of action, so that it can be administered via a single intramuscular injection and still be active 24 hours or more later. For many patients a single injection is sufficient to effect cure. Such a regimen has obvious advantages in a remote rural setting where large numbers of people spread over a wide area must be treated. MSF has published the fruit of more than two decades of experience in a manual on the management of meningitis epidemics. This provides practical guidelines for new field volunteers and local health professionals. Preventing meningitis There are two approaches taken by MSF to the prevention of meningitis outbreaks:
  • vaccination of a population at the beginning of any threatened epidemic. See the article on Managing an epidemic.
  • advocacy on behalf of better living conditions for refugees, who may be at especial risk to outbreaks because of crowding. We recommend that the minimum area of a refugee camp should be 30 square metres per person, with a minimum dwelling space of 3.5 square metres per person. If these conditions are met then rapid contagion is far less likely. An example - epidemic of meningitis in Nigeria Nigeria is a large country in West Africa, with a population of some 110 million. The northern part falls within the meningitis belt, and in early 1996 there was an outbreak of meningococcal disease there that threatened the 50 million inhabitants of the 17 northern states. It was the first time that MSF had been called upon to intervene against meningitis in so densely populated a region. The epidemic lasted approximately four months. The MSF project covered three states, Bauchi, Katsina and Kano. It had the twin objectives of firstly treating meningitis patients rapidly and effectively to prevent death and disability, and secondly cutting off the epidemic before it spread to other parts of the country. At the height of the epidemic MSF had some 50 expatriate field volunteers in country working in collaboration with thousands of Nigerian health workers. To ensure that a maximum number of people across this huge geographical area had access to treatment and immunisation, MSF set up special meningitis centres. A major priority was to strengthen the local cold chain for the storage and transport of the number of vaccines that were needed. Some three million persons were immunised. Almost 46,000 cases of meningitis were recorded in the three states where MSF was active. Almost 5,000 deaths occurred, many of them in isolated villages. To complicate this already overwhelming situation, there were concomitant outbreaks of both cholera and measles that were also taken in hand by the teams. After the end of the epidemic MSF retained a presence in Nigeria to help strengthen epidemiological surveillance How MSF teams treat meningitis patients Ideally, meningitis should be diagnosed by a microscope examination of fluid taken from a patient during a lumbar puncture, which means inserting a needle into the spinal canal low on the back. During an outbreak, however, there is no time to do this on every suspected patient and MSF teams use a clinical case definition: high fever and at least three if the following signs - neck stiffness, headache, vomiting, convulsions, coma or a meningococcal rash. This rash is easily recognised - it looks like bleeding into the skin and is a harbinger of death. In a hospital setting, when only sporadic cases of meningitis must be dealt with, doctors can treat each patient with a regimen of intravenous antibiotics, giving large doses of one or sometimes two drugs several times a day. During a major epidemic, however, it is essential to find more rapid ways of dealing with perhaps several hundred cases each day. The method that has been tested and proven by MSF teams is to use an oily suspension of chloramphenicol, which is an antibiotic that had largely gone out of favour until applied to this particular use. Suspension in an oily base gives the drug a long duration of action, so that it can be administered via a single intramuscular injection and still be active 24 hours or more later. For many patients a single injection is sufficient to effect cure. Such a regimen has obvious advantages in a remote rural setting where large numbers of people spread over a wide area must be treated.