The Gram-negative diplococcus Neisseria meningitidis was first isolated from cerebrospinal fluid (CSF) in the late 1800s. It also was recognized at that time that healthy persons could have carriage without infection.¹ Several different serogroups have since been identified. Those serogroups implicated in causing disease worldwide today include A, B, C, Y, and W-135. In the United States, serogroups B, C, and Y are the most commonly implicated in disease.²

Approximately 2500 to 3500 cases of N meningitidis infection occur annually in the United States, with a case rate of about 1 in 100,000.³ The highest attack rates occur in late winter. Children younger than 5 years are at greatest risk, but another peak in the occurrence of N meningitidis infection occurs in the 15- to 18-year old population.⁴ Other persons at increased risk include those with complement deficiencies and anatomical or functional asplenia. Case mortality rates range from 5% to 13% in the United States.⁵

Large-scale epidemics, most notably in sub-Saharan Africa (the "meningitis belt"), are caused by infection with serogroups A and C. The case rates in the meningitis belt can be as high as 1 in 1000 and 1 in 100 in children younger than 2 years.⁶

In Saudi Arabia in the year 2000, an increase in N meningitidis infection occurred among pilgrims returning from the Hajj and Mecca, according to the World Health Organization. Subsequent follow-up studies by the CDC found an increase in nasopharyngeal carriage in persons returning from Mecca.^7,8

Recently, a hypervirulent strain of serogroup C was discovered in China.⁹ The impact of this new strain is yet to be determined.

PATHOPHYSIOLOGY