All birds can be blood tested for antibodies to this organism and post mortem findings are fairly conclusive. If you are worried about any respiratory problems in your birds please get the bird seen by a vet. All respiratory problems should be treated as an emergency. The signs of Chlamydia infection can vary. Transmission is by respiratory discharges or faeces.
Birds can suffer respiratory signs as above along with conjunctivitis.
Some birds also have an enteritis and a vent discharge. A large percentage of Pigeons will have been exposed to this agent. Many birds can be latently infected. Some imported parrots can be latently infected for many, many years. Chlamydia is a disease that needs to be dealt with some caution.