Causes of Low-Grade Fever and Low White Blood Cell Count in Infants and Young Children

Infants and young children presenting with mild to moderate fever along with low white blood cell count may be caused by the following reasons: 1. **Viral infection**: During viral infections, lymphocytes in the white blood cells participate in the immune response, leading to an increase in lymphocyte count and a relative decrease in neutrophils, which results in an overall lower total white blood cell count. At the same time, viral infections can also cause fever in infants and young children. 2. **Bacterial infection**: Although bacterial infections usually lead to elevated white blood cell counts, in certain cases of severe infection, such as sepsis or pyosepsis, the severity of the infection may suppress the bone marrow hematopoietic system in infants, resulting in a reduced white blood cell count. 3. **Medication effects**: Infants may take certain antipyretic or other medications to manage fever, which may impact their hematopoietic system and lead to a decreased white blood cell count. 4. **Malnutrition or deficiency of certain vitamins**: For example, deficiencies in vitamin B12 or folic acid may affect the normal production of blood cells. 5. **Immune system disorders**: Such as autoimmune diseases, which may cause abnormal white blood cell counts. 6. **Congenital blood disorders**: In rare cases, infants may be born with inherited blood conditions, such as aplastic anemia or leukemia, which could lead to reduced white blood cell counts.