Perhaps you should try some spelling variations:
"complicated case" » "complicated cases", "complicated acute", "complicated chapter"
"communicable diseases" » "communicate diseases", "communicable disease"
"complex diseases" » "complex 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: (("communicable diseases") OR ((("complicated case") OR ("complex diseases")))).
• Removing quotes may allow a broader search: (( communicable diseases ) or ((( complicated case ) or ( complex diseases )))).
• Adding a wildcard symbol may retrieve word variants: (("communicable diseases") or ((("complicated case") or ("complex diseases"))))*.