Infectious Coryza Question

[Northerncreature]

My small flock of four hens got hit by Infectious Coryza last December. I got tests made with the help of a vet and the hen was treated with antibiotics. Unfortunately she did not make it.
The rest of the hens got sick one by one with about 2 months in between. One recovered fully on antibiotics within two weeks while the other went through two rounds of different antibiotics and died back in May. Today, the last of the four started showing symptoms. She’s on antibiotics now and I have learned that if her symptoms don’t subside over the next 2-3 days, there is nothing to be done.
My question is, how can it take 8 months for the disease to go through the flock? From what I’ve read, everyone should be getting sick within a few days. Also, how long does the bacteria stay in the soil? Some sources say 3 weeks, some say 6 months. And how do I disinfect the soil (I can’t really move the run)?
My husband really wants to add new hens to our tiny flock, but I’m not sure this is a good idea right now.

 

[Eggcessive]

Sorry for your loss and the disease. Do not add any new chickens while you still have the others. They are carriers for life, and any chickens you add will get coryza. That is why your others got sick—they were exposed to coryza, and the disease was dormant inside their bodies, but one day became active. Coryza and most other respiratory diseases only last in the environment outside of the hen’s body about 3 days. Only then would I add new healthy chicks, and if possible get them from a hatchery where the chances would be better that they have no diseases. Getting started chicks or pullets from another person still could bring in a contagious disease.