Perhaps you should try some spelling variations:
"_ mean decrease" » "_ means decrease" (Expand Search), "_ mean decreased" (Expand Search), "_ mean increase" (Expand Search)
"50 pp decrease" » "50 pp decreased" (Expand Search), "50 pp increase" (Expand Search)
"_ cd4 decrease" » "_ cd4 decreased" (Expand Search), "_ cd4 increase" (Expand Search)
"a mean decrease" » "a mean decreased" (Expand Search), "a mean increase" (Expand Search)

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("50 pp decrease") OR ((("_ cd4 decrease") OR ((("a mean decrease") OR ("_ mean decrease"))))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"50 pp decrease\") OR (((\"_ cd4 decrease\") OR (((\"a mean decrease\") OR (\"_ mean decrease\"))))))".
• Removing quotes may allow a broader search: (( 50 pp decrease ) OR ((( _ cd4 decrease ) OR ((( a mean decrease ) OR ( _ mean decrease )))))).
• Adding a wildcard symbol may retrieve word variants: (("50 pp decrease") OR ((("_ cd4 decrease") OR ((("a mean decrease") OR ("_ mean decrease"))))))*.