CALCA and Respiratory tract infection: The researcher divided children with respiratory tract infections into bacterial infection group, non-bacterial infection group, and control group, and found that serum SAA, PCT, and CRP levels in the bacterial infection group were 281.34 ± 42.45, 3.28 ± 1.01, and 42.67 ± 11.02, respectively, and serum SAA, PCT, and CRP levels in the bacterial infection group were higher than those in the non-bacterial infection group and in the healthy children, and the difference was statistically significant (p < 0.05) (Yin and Mo, 2022).