CALCA and coinfection: The median serum PCT, CRP, and WBC levels were all significantly higher in the H1N1 with bacterial co‐infection group than in the H1N1‐alone group (median PCT level, 1.46 vs 0.21 ng/mL, P < 0.001; median CRP level, 19.20 vs 5.10 mg/dL, P < 0.001, median WBC count, 8.50 vs 6.90 × 109 cells/L, P = 0.019; Figure 1).