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: Analysis of site of infection showed a preponderance of abdominal infections in liver patients , intrathoracic infections in heart patients , and urinary tract infections in renal patients .
### Output Text:
Analysis of site of infection showed a preponderance of abdominal infections in liver patients , intrathoracic infections in heart patients , and urinary tract infections in renal patients . 