What Is Meningitis?

• Meningitis is the generic term for a bacterial infection of the meninges, a tissue layer that surrounds both the brain and spinal cord. While a range of bacteria species can cause meningitis, the gram-negative, diplococci bacterium known as "Neisseria meningitidis" or simply "the meningococcus" has the transmission ability to create epidemics.
  
  However, not all meningococcus are the same; within the N. meningitidis species, there exist 12 subtypes known as "serogroups," each with its own unique level of damage (lit. "pathogenicity"), triggered immune response in the host (lit. "immunogenicity") and ease of transmission (lit. "epidemiogenicity").
  
  

The Epidemic-Causing Serogroups

• The meningococcal serogroups with the most serious levels of epidemiogenicity are A, B, C and W135. According to the World Health Organization, N. meningitidis B and C cause the majority of infection in Europe and the Americas, A and C cause most African infections, and serogroup A causes almost all of Asia's outbreaks. However, since 2000, a series of outbreaks among Muslims on pilgrimage through Saudi Arabia were traced back to N. meningitidis W135. While not the primary cause of infection in any region, the serogroup Y also has significant epidemiogenic properties.
  
  

How Is Serogroup Determined?

• While vaccines exist for each serogroup, it is essential that physicians administer the vaccine that corresponds to the patients intended travel destination(s). Likewise, if a physician suspects infection, he must administer the antibiotic most effective against the given serogroup.
  
  To determine the serogroup, a sample of spinal fluid is taken from the lumbar region. Once the sample is obtained, several different testing technologies exist. The most reliable method is polymerase chain reaction (PCR), wherein the cells are lysed to release their DNA into solution. After special enzymes (i.e. polymerase) and pre-made, nucleotide sequences called "primers" are added, the solution is gently heated. This causes the bacterial DNA to uncoil and split along its nucleotide-nucleotide hydrogen bonds. The polymerase and primers then work together to copy certain segments of the bacterial DNA. With subsequent heatings, both the original DNA and its copies are copied by the enzymes, causing an exponential growth in their numbers. Finally, the sample is stained and submitted to gel electrophoresis. The resultant band pattern is then compared to those of the various serogroup standards to determine a match.