School-based clusters of meningococcal disease in the United States - Descriptive epidemiology and a case-control analysis

Objective.-To evaluate the epidemiologic features and risk factors for multiple cases of meningococcal disease in schools. Design.-Population-based prospective evaluation and case-control study of clusters of meningococcal disease that occurred in schools from January 1989 to June 1994. Setting.-Surveillance conducted through state health departments in the United States. Main Outcome Measures.-Descriptive epidemiology of school-based clusters of meningococcal disease and determinants of their occurrence. Results.-We identified 22 clusters of meningococcal disease in 15 states. The estimated incidence of secondary meningococcal disease among schoolchildren aged 5 to 18 years was 2.5 per 100 000 population, a relative risk of 2.3 (95% confidence interval [Cl], 1.6-3.3). The median number of students per cluster was 2 (range, 2-4), Of 30 subsequent cases, 10 (33%) occurred 2 or fewer days after the index case, and 22 (79%) occurred 14 or fewer days after the index case. Among the 8 schools with 2 or more cases, 50% of the additional cases occurred 2 or more days after the Second case. Secondary schools (grades 7 through 12) accounted for 15 (75%) of 20 cluster schools compared with 9 (45%) of 20 matched control schools (P<.05). In 16 (73%) of 22 clusters, interaction between case patients was noted. The index patient in cluster schools was more likely than the controls to have participated in a-school-based group activity 14 or fewer days before illness (matched odds ratio, 7.0; 95% Cl, 0.9-57). Conclusions.-Three quarters of the school clusters occurred in secondary schools, with over 70% of subsequent cases occurring within 2 weeks of the index case. Rapid initiation of a chemoprophylaxis program after 2 cases of meningococcal disease in a school would have potentially prevented 50% of subsequent cases in the clusters described.