I'm very sorry about your chick. 
Coccidia is everywhere, and you can't really get rid of it. If it was already in your soil then your older birds have already built resistance to it. Your chicks that recover will be resistant to whatever strain you have. You may have a more virulent strain, or that chick may just have had a weaker system to start with, it's hard to know. I have had outbreaks of coccidiosis in the past. What I do now with all new brooder raised chicks, is starting with the first day they get some dirt from my yard in the brooder in a large plant saucer. They can dig and scratch and peck and dustbathe in it and are that way exposed to all the microbes in the soil from the very beginning and can start building resistance. And the plant saucer is easy to dump and clean. I always have meds on hand when I'm raising chicks so that I can treat quickly if needed, but by exposing them from day one to the soil I have greatly reduced my incidence of outbreak in my flock, it's been about 4 years since I've had an outbreak. When they are in the brooder with no exposure, and then put on the ground when they are older, they have missed the opportunity to build resistance while the immune system is maturing, and it's more likely that they will get sick. Any time you bring in new birds, then it's possible they could bring in a new strain in their digestive tracts, or that they will not be resistant to any strain you have in your soil, so a good idea to watch carefully for symptoms.

Coccidia is everywhere, and you can't really get rid of it. If it was already in your soil then your older birds have already built resistance to it. Your chicks that recover will be resistant to whatever strain you have. You may have a more virulent strain, or that chick may just have had a weaker system to start with, it's hard to know. I have had outbreaks of coccidiosis in the past. What I do now with all new brooder raised chicks, is starting with the first day they get some dirt from my yard in the brooder in a large plant saucer. They can dig and scratch and peck and dustbathe in it and are that way exposed to all the microbes in the soil from the very beginning and can start building resistance. And the plant saucer is easy to dump and clean. I always have meds on hand when I'm raising chicks so that I can treat quickly if needed, but by exposing them from day one to the soil I have greatly reduced my incidence of outbreak in my flock, it's been about 4 years since I've had an outbreak. When they are in the brooder with no exposure, and then put on the ground when they are older, they have missed the opportunity to build resistance while the immune system is maturing, and it's more likely that they will get sick. Any time you bring in new birds, then it's possible they could bring in a new strain in their digestive tracts, or that they will not be resistant to any strain you have in your soil, so a good idea to watch carefully for symptoms.