An article I believe all chicken keepers should read. While the article is attached, I have summarized below:

Dr. Fudge has been an Avian Vet for 42-years, first in California and then South Carolina. During his 42-years of practice, he has never seen a confirmed case of Syngamus Trachea (a.k.a. Gapeworm).

To prove this beyond South Carolina, Dr. Fudge conducted surveys of several labs in multiple States to include; 3-southern States, poultry-certified veterinarians in Atlantic States, and his native State of California pathologist who conducts around 1000 tests per year. All have not had a case of Syngamus Trachea for many years.

He goes on to say that clinical signs seen by owners are generally due to mycoplasma, viruses, bacteria or fungi, and advocates to not treat for worming unless there is proof of infection. While I agree this is good practice, Dr. Fudge is one of only 2-avian vets within 2 1/2 hours from me, and neither are taking new patients.

https://www.backyardchickens.com/attachments/gapeworm-myths-pdf.3344857/