I'm sorry about your damaged immune system NannaMacGeek but, I do think you are bordering on paranoia, but I can understand it due to your condition. I think you are totally overthinking Moocow. It never occurs to me to analyse every glass, cup ,plate, piece of cutlery (ala Hyacinth Bucket... the episode where she ostentatiously wipes the knife and fork on her serviette.)
Starbucks, Costa Coffee et al (along with Mickey D and all the other takeaways) are totally unconcerned about the global effect their throw -away culture is having.
You pays your money , you takes your choice...... ie take your own cup with you and risk the minute chance of picking up a germ , or accept the environmental threat to the planet, and your GCs, GGCs ...and onwards.