You can do your own testing, get a clean bird and expose it to your birds and if it gets what yours had then you know yours are carriers.
just went through that
I called a reliable vet in north portland and his vet tech really didnt know..
I asked if they could call me back if they did have a blood test to rule why my DD little red hen sneezes with no other symptom.
The EE we have has injured her R eye and it foams up now and then the other eye is fine.. so I am still waiting to hear back from the vet
at least now I know that I can call the Oregon vet a OSU.. my flock was already intergrated when my two big girls got wheezy and sneezy 14 days of duramyacin cured that...
best of luck