Perhaps you should try some spelling variations:
"communicate diseases" » "communicable diseases", "communicated disease", "communicable disease"
"complicated diseases" » "complicated cases", "complex diseases", "complicated case"
"mediated diseases" » "related diseases", "medical diseases", "related disease"

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 ((("complicated diseases") OR ("mediated diseases")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"communicate diseases\") or (((\"complicated diseases\") OR (\"mediated diseases\"))))".
• Removing quotes may allow a broader search: (( communicate diseases ) or ((( complicated diseases ) OR ( mediated diseases )))).
• Adding a wildcard symbol may retrieve word variants: (("communicate diseases") or ((("complicated diseases") OR ("mediated diseases"))))*.