IL6 and infection: Compared with the mild group, most patients in the severe group showed higher levels of infection-related indicators, such as procalcitonin (0.07 vs. 0.05, P < 0.001), C-reactive protein (3.2 vs. 0.6, P < 0.001), interleukin-6 (9.4 vs. 3.2, P < 0.001) and erythrocyte sedimentation rate (52.0 vs. 34.0, P < 0.001), indicating that inflammation was more prominent in severe cases.