In the tropics, Bacterial meningitis is a biggie! Cyclical epidemics of meningococcal disease occur every 5 to 7 years in the ‘Meningitis Belt’ – 21 countries from Senegal to Ethiopia. An estimated 1 – 2% of people may be affected during such epidemics.
The majority of pyogenic meningitis cases are caused by (i) the pneumococcus bacteria Streptococcus pnuemoniae, of which there are several serogroups, (ii) the meningococcus bacteria Neisseria meningitidis or (iii) Haemophilus influenzae b (Hib). All three are common in children under 2 years. The epidemiology of meningitis will vary between countries and therefore it is important to determine the causative organisms at the place of medical practice, e.g. Streptococcus suis is the most common causative pathogen for bacterial meningitis in Vietnam.
All three major causes of bacterial meningitis can be prevented by vaccines based on the serogroup specific antigens. Annoyingly, they are less immunogenic in the groups most at risk (children under 2 years of age). New conjugate vaccines – a vaccine containing bacterial caspsular polysaccharide joined to a protein to enhance immunogenicity – seem more successful despite the heavier price-tag.
Cryptococcal meningitis in the tropics now mostly occurs in HIV-infected patients. In such cases, the CSF is typically under high pressure with raised protein level and lymphocytosis. Raised intracranial pressure is associated with a poor prognosis. Mortality is high, even with optimum treatment.
There are currently on posts about bacterial meningitis just yet, but watch this space!