What's the likelihood of long term antibiotic prophylaxis resulting in pulmonary fibrosis with nitrofurantoin? mom's getting sequentially recurrentuti

Pulmonary fibrosis : Pulmonary fibrosis due to nitrofurantoin is rare, about less than 1% reported in literature, but risk increases with age of patient and other medical condition. Symptoms may start to develop after 6 months of treatment. Usually fatigue, dry cough and shortness of breath without fever. Stop the nitrofurantoin if these symptoms develop and see a physician immediately