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: The incidence of Reye syndrome in New South Wales , Australia , is estimated from this study to be approximately nine cases per 1 million children compared with recent US data of ten to 20 cases per 1 million children and three to seven cases per 1 million children in Great Britain .
### Output Text:
The incidence of Reye syndrome in New South Wales , Australia , is estimated from this study to be approximately nine cases per 1 million children compared with recent US data of ten to 20 cases per 1 million children and three to seven cases per 1 million children in Great Britain . 