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: During the 30 - day follow - up period , no patients died of a cardiovascular event ( 0 % ; 95 % CI , 0 - 6 . 1 % ) and no patient sustained a nonfatal myocardial infarction ( 0 % ; 95 % CI , 0 - 6 . 1 % ) .
### Output Text:
During the 30 - day follow - up period , no patients died of a cardiovascular event ( 0 % ; 95 % CI , 0 - 6 . 1 % ) and no patient sustained a nonfatal myocardial infarction ( 0 % ; 95 % CI , 0 - 6 . 1 % ) . 