I found this info online:
Viral infections, including chickenpox, parvovirus, hepatitis C, Epstein-Barr, mononucleosis, or HIV
- Severe bacterial infection in your blood
Blood cancer such as leukemia or lymphoma
A problem with your bone marrow
Rare disorder called hemolytic uremic syndrome
Miliary tuberculosis (miliary TB)
Vitamin B12 or folate (vitamin B9) deficiency