systematic, systemic

Systematic or systematic means having, using, displaying, or invloving a method or plan--
Let's use a systematic approach--we'll go through every name on the list alphabetically.
This would be easier if you'd be more systematic--put all the files you've checked in one pile, for a start.

Systemic or systemic is most commonly used as a medical term, meaning involving the entire body, through the bloodstream or system--
If the disease is systemic, it may be nearly impossible to cure.
Infections left untreated can become systemic, with serious consequences.

Now that you know that, you can say--
"We need a systematic way of checking for the presence of systemic infection."