Several different bacteria can cause meningitis but Neisseria meningitidis -- which is to blame for this outbreak -- is one of the most significant because of its potential to cause epidemics.

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Both bacteria can cause meningitis, pneumonia, and other infections.

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The risk to the families of pilgrims was highlighted by a study in Malaysia, published in 2002: among people sharing a house with a returning pilgrim, about 8% were carrying traces of the bacteria associated with meningitis.

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In children who are vaccinated, it eliminated most of the pneumonia and meningitis that bacteria causes.

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The vaccines immunize children against two different bacteria that cause pneumonia and meningitis.

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Meningitis is an aggressive disease when bacteria invade the protective membranes of the central nervous system and cause adverse inflammatory responses.

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