Infection is not a nursing diagnosis according to NANDA's most recent publication.
Do you have any assessment data?
What are their vital signs? With sepsis you could have everything from depressed temp. to elevated temp. Oxygenation? BP (usually low BP is a symptom of sepsis)?
You get my point. You are assessing the patient as a whole. So a medical diagnosis in itself can point you in the right direction for what complications you need to monitor, but you, the nurse, still need to assess. You know the patient is depressed so I bet you know much more.
Their impaired VERBAL communication will be r/t the alteration of the CNS then you need to add the defining characteristics: aphasia perhaps? None the less it is unlikely that the impaired verbal communication is going to be in your top few NDs.
If you are looking for priority NDs then you should always consider ABCs -- you should always consider these anyway. If you post some of your assessment data we could probably help you more.
As for looking up conditions Google "family practice notebook", Mayo Clinic or Cleveland Clinic. Still your nursing textbook
often have the NDs for conditions listed.