Fig. 1.

(a) Workplace data (thick black line, left axis) and university data (thin grey line, right axis) over time. ILI, influenza-like illness. (b) Proportion of each total population over time, where the number of employees absent is given for the workplace (thick black line) and the number of reported cases is given for the university (thin grey line). The workplace was closed on Thanksgiving Day, 26 November 2009. The university was not in session for the Thanksgiving holiday from 23 to 27 November 2009, and the student health centre was closed from 26 to 29 November 2009.