As a Carer for both Ros my Wife who has MS and Dementia and my Mum who has 2 forms of dementia and a failing heart, Covid is proving a big challenge. We still have to have 2 Carers, 4 times daily to manage Ros. Years of Caring plus a bad Car accident means I can do little of the moving & handling needed to let Ros to stay at home. My worry is that because we live outside a Care or Nursing home, our Carer Workers are not being routinely tested. It feels a bit like pot luck if we get Covid or not. To some extent it feels as if we have been left to our fate. 
Good morning Norman
Are you able to speak with the care agency. To only send carers who have taken regular testing. Alternately could you purchase a no touch thermometer. And ask the agency if you would be allowed. To check the carers temperatures before entering you home.
I know this is not necessarily ideal but it could help to alleviate your anxiety. Which you are well entitled too have.
We all have to do what we think is best for our families.
Also this is only one useful tool. And carers still need to wear their PPE and wash their hands etc.
I feel the same way Norman, I am starting to feel it would be safer if my mother was in a care home rather than having carers coming and going, the high turn over of staff within the care company means there are new carers appearing every few weeks. Care at home seems to have been been forgotten about!