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