Perhaps you should try some spelling variations:
"complicated diseases" » "complicated cases", "complex diseases", "complicated case"
"mediated diseases" » "medical diseases", "related disease"
"related diseases" » "related disorders"
"communicable diseases" » "communicate 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: (("communicable diseases") OR ((("complicated diseases") OR ((("mediated diseases") OR ("related diseases")))))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"communicable diseases\") or (((\"complicated diseases\") or (((\"mediated diseases\") OR (\"related diseases\"))))))".
• Removing quotes may allow a broader search: (( communicable diseases ) or ((( complicated diseases ) or ((( mediated diseases ) OR ( related diseases )))))).
• Adding a wildcard symbol may retrieve word variants: (("communicable diseases") or ((("complicated diseases") or ((("mediated diseases") OR ("related diseases"))))))*.