Hello,
I have gone through your query and understand your concern.
It is very usual to have the High Neutrophils and Low
Lymphocyte count in any viral infection.
Fifth disease is a Viral Infection by virus called Human Parvo virus B19.
As you have already confirmed Fifth disease by your treating doctor.
Our focus should be on further treatment.
There is no special treatment for Fifth disease.
Antibiotics will not help, because it is not a bacterial infection.
As he have swollen joints and pain in hands and knees , he may need Non Steroidal Anti inflammatory drugs like
Paracetamol.
Give him Plenty of oral fluids and rest.
As the rashes are appeared, It no more spread to others.
Now he can go to school and play with other children.
Hope this helps.
Please write back for further queries.
Wishing you good health.