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: METHODS : We included data from people participating in the Vancouver Injection Drug Users Study who reported injecting illicit drugs at least once in the month before enrolment , lived in the greater Vancouver area , were HIV - negative at enrolment and completed at least 1 follow - up study visit .
### Output Text:
METHODS : We included data from people participating in the Vancouver Injection Drug Users Study who reported injecting illicit drugs at least once in the month before enrolment , lived in the greater Vancouver area , were HIV - negative at enrolment and completed at least 1 follow - up study visit . 