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: Using as the reference group women who were not using oral contraception , had no recent pregnancy or menopausal symptoms , the case - control analysis gave an adjusted odds ratio ( OR ( adj ) ) of 7 . 44 ( 95 % CI 3 . 67 - 15 . 08 ) for CPA / EE use compared with an OR ( adj ) of 2 . 58 ( 95 % CI 1 . 60 - 4 . 18 ) for use of conventional COCs .
### Output Text:
Using as the reference group women who were not using oral contraception , had no recent pregnancy or menopausal symptoms , the case - control analysis gave an adjusted odds ratio ( OR ( adj ) ) of 7 . 44 ( 95 % CI 3 . 67 - 15 . 08 ) for <span class="chemical">CPA</span> / <span class="chemical">EE</span> use compared with an OR ( adj ) of 2 . 58 ( 95 % CI 1 . 60 - 4 . 18 ) for use of conventional COCs . 