Figure 1. . Outbreak of Neisseria meningitidis serogroup W135, Central River and Upper River Regions, The Gambia, February 1–June 25, 2012. A) Attack rate per 100,000 persons per week. B) Attack rate per 100,000 children <5 years of age per week. Light gray bars, Central River Region; dark gray bars, Upper River Region. Alert threshold corresponds to an attack rate of 5; epidemic threshold, to an attack rate of 10.