In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: BACKGROUND : Studies on the association between the long - term use of aspirin and other analgesic and nonsteroidal anti - inflammatory drugs ( NSAIDs ) and end - stage renal disease ( ESRD ) have given conflicting results .
### Output Text:
BACKGROUND : Studies on the association between the long - term use of <span class="chemical">aspirin</span> and other analgesic and nonsteroidal anti - inflammatory drugs ( NSAIDs ) and end - stage renal disease ( ESRD ) have given conflicting results . 