I think the article bellow is interesting if you have neutropenia.
Neutropenic Precautions Demystified
http://www.clinicalcorrelations.org/?p=745
You have in your body 10 times more microbial cells than human cells. (
https://en.wikipedia.org/wiki/Microbiota ). When you are with neutropenia these bacterias that live peacefully, for instance , in your gut can go to other parts of your body and cause infections because your immune system is not working normally.
The majority of infections in neutropenic patient are caused by bacterias inside his own body. I do not remember where I read, but something like 80% of infections are caused by these bacterias that are already inside our body.