Andreanar... I say this again because you seem to be very stricken by this even on the outside chance your birds were the source.... There is no way (not even a small chance) your chicks were the cause of that infection. Coccidiosis is present in all chicken situations. The addition of healthy looking chicks to this other persons flock, could certainly infect the new flock in theory. But would not be the cause of death in an older chicken in the space of 5 days. The life cycle of the organism is longer than 5 days to begin with. To cause what you describe, the organism would have had to already be thickly present within that third flock. (The one with all the symptoms and the fatality). You practiced good bio-security.
1. Chicks that had lethal doses of CC would not have looked healthy to someone paying attention. . And 2. even if you dropped a lethally infected chick into that flock, it would be hard pressed to cause death and diarrhea on the order you describe within 5 days. The person with the dead chicken is likely the one with the most lax biosecurity and that is why it is throughout her flock. Swapping birds back and forth is not a good idea and this is the reason. I would bet the chicks you had were likely just the latest additions to that flock and I would be willing to say that in that short space of time, your chicks could not have been the cause of those sick birds.
