There were no significant differences in the median duration of cough : 10 days among patients with CRP concentrations < 8 mg/l [ 95 % confidence interval ( CI ) : 8-11 days ] , 11 days among those with concentrations ranging from 8 to 19 mg/l ( 95 % CI : 8-16 ) and 11 days in those with CRP > 20 mg/l ( 95 % CI : 9-12 ) ( P = 0.337 ) .