Perhaps you should try some spelling variations:
infections diseases » infectious diseases, infectious disease, infection disease
infections disease » infectious disease, infection disease, infectious diseases
infection diseases » infectious diseases, infectious 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: ((((infections diseases) OR (infections disease))) OR (infection diseases)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((infections diseases) OR (infections disease))) or (infection diseases))".
• Adding a wildcard symbol may retrieve word variants: ((((infections diseases) OR (infections disease))) or (infection diseases))*.