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