Geographic differences in bacterial meningitis: Less may be as interesting as more

Many reports in the last decade have described populations with a high incidence of bacterial meningitis, especially amongst indigenous groups in industrialised countries, such as North American Eskimos and Apache Indians and Australian Aborigines, particularly with meningitis due to Haemophilus influenzae type b (Hib). Lack of evidence that invasive Hib disease, including meningitis, is a significant health problem has been attributed to lack of appropriate data, either due to lack of laboratory and clinical facilities, such as in most less industrialised countries, or lack of study. Host differences in immune response, though known to be important for individual susceptibility to Hib disease and bacterial meningitis, have not been thought important on a population level. Good quality epidemiologic data now available from Hong Kong and Japan, based on sound laboratory methods, have shown bacterial meningitis, particularly due to Hib and Neisseria meningitidis, to be significantly less common than in predominantly Caucasian populations in various industrialised countries. Differences in host immune response to these capsular polysaccharides seems the most likely explanation for this observation. It is interesting that other immunologically mediated disorders such as Kawasaki disease acid systemic lupus erythematosis have a relatively high incidence in Sine Japanese populations, lending plausibility to inherited differences in immune response as a mechanism for these observations.