Serogroup C meningococcal outbreaks in the United States. An emerging threat.

Multiple outbreaks of serogroup C Neisseria meningitidis have recently been reported from diverse areas of the United States. To better define the characteristics of this increasingly important problem, we reviewed data on all known serogroup C outbreaks in the United States from January 1980 through June 1993. MEDLINE searches, Centers for Disease Control and Prevention records, state health department officials, infectious disease experts, and the meningococcal vaccine manufacturer. DEFINITION OF AN OUTBREAK: Three or more cases of serogroup C meningococcal disease within a 3-month period, either among members of a community or persons attending a single school or other institution, for which those cases represented an attack rate of at least five per 100,000 population. Twenty-one outbreaks of serogroup C meningococcal disease were identified; eight occurred since 1991. In 1992 and the first half of 1993, approximately 180,000 doses of vaccine were administered for outbreak control, compared with approximately 34,000 doses from 1980 to 1991. Approximately 50% of community-outbreak cases were between the ages of 5 and 24 years, compared with only 19% of sporadic serogroup C cases (P < .001). Subtyping of patient isolates indicates that outbreaks are clonal; however, at least five distinct but closely related strains have caused recent outbreaks. Serogroup C outbreaks are occurring more frequently in the United States. The effectiveness of preventive measures depends on early recognition; therefore, physicians should promptly report all cases of suspected meningococcal disease, and the causative serogroup should be established for every case.