Meningitis epidemiology and demographics


 * Associate Editor(s)-In-Chief:

Epidemiology


Meningitis refers to the inflammation arachnoid matter, the sub-arachnoid space and the cerebrospinal fluid (CSF, including the ventricles). Meningitis can affect anyone in any age group, from the newborn to the elderly.

From its recognition in 1805 until the early 20th century, bacterial meningitis was virtually uniformly fatal. Until recent years, up to 50% of patients who survived the acute infection would be left with permanent sequelae such as mental retardation and hearing loss. Over the past several years, there has been a striking shift in the demography of meningitis.
 * In 1986, the median age of a patient with meningitis was 15 months, as compared with 25 years in 1995.
 * Before the widespread use of the conjugated Haemophilus influenzae type B (HIB) vaccine in 1990, H. influenzae type b meningitis developed in nearly 1 in 200 children < 5 years old, and almost 70% of the cases of meningitis in children < 5 were due to H influenzae.
 * It was necessary to conjugate the H. influenzae type b polysaccharide to a carrier protein in order to make a T-cell dependant antigen that could induce an immune response in infants.
 * In the study by Schuchat et.al. in 1995, H. influenzae only accounted for 7% of cases.
 * The case-fatality rate varied significantly amongst the different organisms, and the pathogenic organisms responsible for disease varied greatly with age.
 * Group B Streptococcus agalactiae (S. agalactiae) was the main cause of meningitis in infants < 1 month with Listeria accounting for ~ 20% of cases.
 * In infants 1 month – 23 month of age, Streptococcus pneumoniae (S. pneumoniae) and Neisseria meningitidis (N. meningitidis) caused 45% and 31% of the cases, respectively.
 * In the 2 – 18 year old age group, N. meningitidis caused 59% of the cases, and in people 19 – 59 years old S. pneumoniae caused 62% of the cases.
 * Nosocomial infections with Gram-negative bacilli are becoming increasingly important as well.

The "Meningitis Belt" is an area in sub-Saharan Africa which stretches from Senegal in the west to Ethiopia in the east in which large epidemics of meningococcal meningitis occur (this largely coincides with the Sahel region). It contains an estimated total population of 300 million people. The largest epidemic outbreak was in 1996, when over 250,000 cases occurred and 25,000 people died as a consequence of the disease.