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