Evaluation of the use of mass chemoprophylaxis during a school outbreak of enzyme type 5 serogroup B meningococcal disease

Background. A vaccine for prevention of serogroup B meningococcal disease is not available in the United States, and indications for the use of mass chemoprophylaxis for control of meningococcal outbreaks are not well defined. In response to an outbreak of six cases of enzyme type 5 serogroup B meningococcal disease among students at a middle school, we implemented a program of mass rifampin prophylaxis and evaluated the effectiveness of this preventive measure. Methods. Oropharyngeal cultures were obtained from 351 of the 900 students before prophylaxis; 196 participants were recultured 3 weeks later. Meningococcal isolates were subtyped and tested for rifampin susceptibility, and risk factors for disease or carriage among students were evaluated. Results. No cases occurred after prophylaxis. Before prophylaxis 10% (34 of 351) of students were meningococcal carriers and 3.4% (12 of 351) carried the epidemic strain. After prophylaxis 2.5% (5 of 196) were carriers and 1.0% (2 of 196) carried the epidemic strain. Rifampin was 85% effective in eradicating carriage, and the rate of acquisition of carriage during the 3-week period was low (0.5%). Carriage persisted after prophylaxis in 4 students; 3 of these postprophylaxis isolates were rifampin-resistant. Rifampin resistance thus developed in 12% (3 of 26) of preprophylaxis isolates. Disease/epidemic strain carriage was associated with enrollment in the school band and certain other classes. Conclusions. These findings suggests that mass chemoprophylaxis may be effective and should be considered for control of school serogroup B meningococcal outbreaks. This approach is less likely to be effective for control of outbreaks affecting larger, less well-defined populations and is associated with the rapid development of antibiotic resistance.