Antigen detection systems in the laboratory diagnosis of bacterial meningitis
The rapid and precise diagnosis of bacterial meningitis is important because of its potential severity and relative frequency. Leading causes in the United States include Haemophilus hlfluetzzae type b, Streptococcus pneutnoniae, Neisseria tnenhlgitidis, Escherichia coli and Streptococcus agalactiae (group B Streptococcus). Bacterial meningitis, unlike many infectious processes, is rarely self-limited. Prompt chemotherapeutic intervention, therefore, is important when clinical signs of meningitis become apparent. A tentative etiologic diagnosis may be made on the basis of the patient's condition and age-specific incidence or epidemiologic factors, but the exact diagnosis depends on immunodiagnostic or microbiologic test results. Moreover, these results must be made available in a timely fashion to positively influence clinical decisions. While methods in clinical chemistry and hematology laboratories have achieved a status permitting the needed speed, the same has not been accomplished in clinical immunology and microbiology. There have been few tests available, with the exception of the Gram stain or another direct microscopic approach, to make an immediate etiologic diagnosis of bacterial meningitis. It is important to recognize that the value of a Gramstained smear of cerebrospinal fluid (CSF) for diagnosis of meningitis should not be forgotten. The sensitivity of the direct microscopic examination of CSF is at least 75%. Tests that rely on detection of bacterial antigens, rather than on growth of an organism, potentially offer not only speed equivalent to that of the Gram stain but greater specificity and sensitivity.