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.