Perhaps you should try some spelling variations:
"communicate diseases" » "communicable diseases", "communicated disease", "communicable disease"
"mediated diseases" » "related diseases", "related disease"
"medical diseases" » "tropical diseases", "viral diseases"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("communicate diseases") OR ((("mediated diseases") OR ("medical diseases")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"communicate diseases\") or (((\"mediated diseases\") OR (\"medical diseases\"))))".
• Removing quotes may allow a broader search: (( communicate diseases ) or ((( mediated diseases ) OR ( medical diseases )))).
• Adding a wildcard symbol may retrieve word variants: (("communicate diseases") or ((("mediated diseases") OR ("medical diseases"))))*.