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Epidemiology and Meningococcal Serogroup Distribution in the United States

Meningococcal disease is a serious life-threatening illness resulting from infection with the bacterium Neisseria meningitidis (N. meningitidis). Following the development of vaccines against Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae, N meningitidis is now the leading cause of bacterial meningitis in young children in the United States. Each year, approximately 1000 to 3000 cases of meningococcal disease occur within the United States. In the general population, meningococcal incidence rates range between 0.5 and 1.1 per 100,000 population. However, incidence rates of meningococcal disease vary among age groups. Incidence rates are highest during the first year of life. Thereafter, rates begin to decrease before increasing again in 15 to 24 year-olds. During the years of 1998 to 2007, infants (typically defined as a child under 1 year of age) had the highest rate of disease (5.38 per 100,000 population). A second peak in incidence of meningococcal disease occurred in adolescents aged 14 to 17 years (0.74 per 100,000 population) and those aged 18 to 24 years (0.76 per 100,000). The Summary of Notifiable Diseases (United States) for 2007 show infants had a disease rate of 3.37 per 100,000, whereas 15 to 24 year-olds had a rate of 0.53 per 100,000 population. Similarly, surveillance data from 2007 and 2008 show adolescents between the ages of 11 and 17 years had a disease incidence of 0.14 and 0.11 per 100,000 population, respectively. Pathogenic strains of N meningitidis are classified into serogroups based on the immunologic reactivity of their polysaccharide capsule, a structure that surrounds the inner and outer membrane of the bacteria. There are 13 different serogroups, but only 5 are typically involved in invasive disease. The most common types associated with disease in the United States are B, C, and Y. This manuscript reviews the distribution of serogroups in the United States and the potential impact that may result if changes in distribution occur.