Age frequencies of case and control participants.

Many participants did not know their age, and approximate ages were assigned to many subjects, leading to large spikes of numbers at 30, 40, 50, and 60 years, with minor spikes at 5-year intervals. These spikes were smoothed using a moving-window average over 10 years. The mean ages of Trypanosoma brucei gambiense and T. b. rhodesiense case and control participants were 36 and 42, respectively. The age distributions were similar except that the T. b. rhodesiense subjects’ ages were shifted to the right.