I think it's a common euphemism, similar to referring to "subjects" as "participants" and so on.

- https://link.springer.com/referenceworkentry/10.1007%2F978-3...

- https://az.research.umich.edu/medschool/glossary/double-mask...

- https://aidsinfo.nih.gov/understanding-hiv-aids/glossary/211...