Causes Of Low White Blood Count

they had a WBC count of only 1.7

That's how low. Leukemia is really the first and the main reason. Going through chemo or radiation treatments would be. Other autoimmune diseases.
To put this in perspective 4.5 is the lower end of normal. You should also note that this number is in scientific notation. So 1.5 is really 1.5 x10 to the third, which translates to 1500. This is useful to know if you search online and see it written this way.
This person is extremely sensitive to infections this account. Please tell them to make sure they wash their hands frequently and cook all food thoroughly.

http://www.mayoclinic.com/health/low-whi ...

http://www.diagnose-me.com/cond/C270145. ...