Cystic fibrosis (CF) is thought to be a genetic disease, arising in infants and young children. In CF, the pulmonary epithelial cells are immunologically impaired, and lung tissue produces copious amounts of mucous, pus, and sputum, clogging the lung.  CF patients have consolidation of pus in the lower lung, low oxygen levels, microscopic inclusion cysts, scarring in the lung, and co-morbid gastrointestinal disease. The average lifespan of a CF patient is 37 years old.

Chlamydia pneumonia was found in CF patients suffering an exacerbation. Improvement in CF was observed with long-term (3-6 months) macrolide therapy, which was assumed to provide an anti-inflammatory effect. The effectiveness of macrolides supports CF as a lung infection; and the persistence of the infection with long-term macrolide therapy suggests immortal pathogens.

CF can be caused by immortal pathogens acquired in utero or in early childhood. The presentation of CF is similar to chlamydia pneumonia, chlamydia trachoma, or both, infecting the lung. CF patients are often treated with penicillin and/or broad-spectrum antibiotics, for recurrent lung infections, which can change the shape and extend the lifespan of chlamydia pathogens, make the pathogens more difficult to treat, induce antibiotic resistance, and lessen microbial diversity. Testing all CF patients for a wide variety of pathogens; and treating CF patients with medications effective against the pathogens, may improve the effectiveness of treatment.

https://www.nice.org.uk/advice/esuom37/chapter/key-points-from-the-evidence

https://erj.ersjournals.com/content/33/2/360