Increased case-fatality rate associated with outbreaks of Neisseria meningitidis infection, compared with sporadic meningococcal disease, in the United States, 1994-2002

Background. Outbreaks of meningococcal disease are infrequent but important public health events. We characterize outbreak-associated cases in the United States and compare them with sporadic disease. Methods. Outbreaks of meningococcal disease that occurred during the period of 1 July 1994 through 30 June 2002 were identified through state health departments, Centers for Disease Control and Prevention records, and a review of newspapers and the medical literature. Cases associated with outbreaks were compared with sporadic cases identified through population-based surveillance. Results. We identified 69 outbreaks of Neisseria meningitidis infection ( median, 9.5 outbreaks per year; range, 3-14 outbreaks per year), which involved 229 patients from 30 states. Forty-three ( 62%) of the outbreaks involved N. meningitidis serogroup C, 17 ( 25%) involved serogroup B, and 9 ( 13%) involved serogroup Y. Twenty-five outbreaks ( 36%) occurred in communities, and 44 ( 64%) were organization based, including 12 that occurred in colleges and universities, 19 that occurred in primary and secondary schools, and 8 that occurred in nursing homes. Vaccination campaigns ( with the A/C/Y/W-135 meningococcal polysaccharide vaccine) were conducted for 31 outbreaks ( 28 involving serogroup C and 3 involving serogroup Y). After controlling for age, serogroup, and clinical presentation, outbreak-associated cases were associated with a higher case-fatality rate than were sporadic cases ( 21% vs. 11%; odds ratio, 3.3; 95% confidence interval, 2.0-5.5). Conclusions. Outbreaks remain an important but infrequent public health issue, representing < 2% of all cases of meningococcal disease. However, given the increased case-fatality rate found among outbreak- related cases of N. meningitidis infection, additional investigation of factors that favor the transmission and virulence of outbreak-related strains is warranted.