Explode is for including related narrower terms in your search, along with major concepts to make sure no articles are overlooked because the subject heading used was a subheading.
This allows you to get results from all three subject headings in one search.
|CINAHL Headings Search for articles about:
|# of Results
|Cross Infection CINAHL Heading Alone:
|Cross Infection CINAHL Heading + Explode:
|Cross Infection, Catheter Related Infections, Healthcare-Associated Pneumonia, Pneumonia, Ventilator- Associated