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: In 44 ( 62 . 8 % ) patients , ATT was prescribed empirically without definitive evidence of tuberculosis .
### Output Text:
In 44 ( 62 . 8 % ) patients , ATT was prescribed empirically without definitive evidence of tuberculosis . 