Weekly illness-like illness (ILI) counts by Early Aberration Response System to detect the onset of the influenza epidemic during the 2007–08 season, Beijing, People's Republic of China. Triangles and diamonds represent different alert situations—C1-mild (C1), C2-medium (C2), and C3-ultra (C3)—automatically generated by the reporting system: triangle, C2C3; open diamond, C3; and solid diamond, C1C2C3.