MENINGOCOCCAL INFECTION

Meningococcal infection, first recognized nearly 2 centuries ago as epidemic cerebrospinal fever, occurs worldwide as sporadic, endemic, and epidemic cases. Worldwide, most cases are caused by serogroups A and C, whereas in the United States, serogroups B and Y predominate (see “Culture and Laboratory Findings”). Humans are the only natural host for the bacteria. Transmission of the organism occurs from person to person by direct contact with contaminated respiratory secretions or airborne droplets with subsequent colonization of the nasopharynx. Nasopharyngeal carriage approximates 5% to 15% in nonepidemic periods but may approach 50% to 95% during epidemics, especially serogroup A epidemics. The carriage rate is also increased when there is crowding, such as in military barracks, dormitories, prisons, convocations, and sporting events. The oropharyngeal and nasopharyngeal carriage may persist for several weeks to several months. Sexual transmission of meningococci in women and homo sexual men may result in anogenital carriage. Most cases of disease (eg, bacteremia, meningitis) occur in children between 6 months and 5 years of age. With few exceptions, invasive meningococci have a polysaccharide capsule that forms the basis for serogrouping of strains. Invasive disease occurs almost exclusively in persons who lack specific antimeningococcal antibody to the colonizing meningococcal strain. Individuals with complement component deficiencies are at an increased risk for developing invasive meningococcal infections because their serum loses the ability of complement-antibody mediated lysis of the bacteria.