> It's just not a serious part of the discussion, and it is likely invoked as an attempt to cast certain classes of foreigners as unclean and trigger susceptible people's disgust response.

The CDC literally has policies about who can be admitted to the U.S. as an immigrant or refugee based on their health status[1], including whether or not they are carrying a communicable disease (such as TB).

This unsubstantiated inference about other people's intentions is misguided at best, and disingenuous at worst.

[1]https://www.cdc.gov/immigrantrefugeehealth/exams/medical-exa...