Finally, 14 risk factors were found to have statistical significance for the development of BO after ADV pneumonia (P < 0.05): coinfection with other viruses, tachypnea, wheezing, respiratory support, length of wheezing days, length of fever days, hospitalization days, LDH levels, PCT values, C3 values, CD4+ T-cell proportion, CD8+ T-cell proportion, T lymphocyte proportion and B lymphocyte proportion (Table 4). Here, CD4 is linked to pneumonia.