The natural history and genetic diversity of Haemophilus influenzae infecting the airways of adults with cystic fibrosis

Haemophilus influenzae is a Gram-negative pathobiont, frequently recovered from the airways of persons with cystic fibrosis (pwCF). Previous studies of H. influenzae infection dynamics and transmission in CF predominantly used molecular methods, lacking resolution. In this retrospective cohort study, representative yearly H. influenzae isolates from all pwCF attending the Calgary Adult CF Clinic with H. influenzae positive sputum cultures between 2002 and 2016 were typed by pulsed-field gel electrophoresis. Isolates with shared pulsotypes common to ≥ 2 pwCF were sequenced by Illumina MiSeq. Phylogenetic and pangenomic analyses were used to assess genetic relatedness within shared pulsotypes, and epidemiological investigations were performed to assess potential for healthcare associated transmission. H. influenzae infection was observed to be common (33% of patients followed) and dynamic in pwCF. Most infected pwCF exhibited serial infections with new pulsotypes (75% of pwCF with ≥ 2 positive cultures), with up to four distinct pulsotypes identified from individual patients. Prolonged infection by a single pulsotype was only rarely observed. Intra-patient genetic diversity was observed at the single-nucleotide polymorphism and gene content levels. Seven shared pulsotypes encompassing 39% of pwCF with H. influenzae infection were identified, but there was no evidence, within our sampling scheme, of direct patient-to-patient infection transmission.