After our coyote issues, I read quite a bit and learned that many scientists believe that the coyote may not actually be nocturnal. Instead, it has chosen to become active during the night where there is human pressure.
Wherever they are not hunted or harassed, they become more active during the day whereas animals like raccoons, etc., still prefer to be active at night regardless of what people are doing.
I'd say a coyote out during the day is likely bad news, not because of the potential for disease, but because of its lack of fear of humans. Watch your children and animals. Reports of bold behavior generally precedes attacks in urban areas where they've been a problem.