The presence of low white blood cells in babies with fever is usually due to a virus, but it can also be caused by a mycoplasma infection, or a serious bacterial infection. If the patient’s white blood cells are reduced and the C-reactive protein, calcitoninogen, and mycoplasma antibodies are normal, then a viral infection, such as oseltamivir against influenza virus, etc., is considered. If the patient’s C-reactive protein and calcitoninogen increase, it is considered to be a severe bacterial infection with reduced white blood cells, which needs to be treated with antibiotics, such as cefixime, amoxicillin, azithromycin, etc. If the patient’s C-reactive protein and calcitoninogen increase, it is considered to be a severe bacterial infection with reduced white blood cells. If the C-reactive protein and calcitoninogen are normal, but mycoplasma antibodies are more than four times elevated, this is considered to be due to atypical pathogenic bacteria, and treatment with macrolide azithromycin, erythromycin and other related drugs is required.