Serogroup B invasive meningococcal disease (IMD) outbreak at a Japanese high school dormitory: An outbreak investigation report from the first IMD outbreak in decades.

Abstract Purpose The first outbreak of invasive meningococcal disease (IMD) in decades occurred in a high school dormitory in 2011. This report aims to describe the results of the IMD outbreak investigation and to discuss current issues of IMD in Japan. Methods We conducted an epidemiological and microbiological investigation against the IMD outbreak of serogroup B among students and staff in a high school dormitory. Information on patients was collected to analyze risk factors for IMD. Control measures and public health actions were summarized. Results Three cases of meningitis and two cases of bacteremia were identified. Freshmen (15–16 years old) living in the dormitory with preceding cough were high-risk populations in this outbreak. Pulsed-field gel electrophoresis, multilocus sequence typing, and porA gene sequencing results revealed that all isolates were closely related to each other and had deep similarities to the domestic circulating meningococcal strain. The outbreak was terminated after promptly implementing control measures. Based on the results of our investigation, from April 2013, national infectious disease surveillance started to target meningococcal bacteremia as part of IMD, in addition to meningococcal meningitis, which was newly designated as a category II school infectious disease under the School Health and Safety Act. Conclusions This outbreak has enhanced public health measures against IMD in Japan. The development of national guidelines for appropriate public health interventions on the IMD outbreak response including chemoprophylaxis is still needed.