title: Airway bacterial concentrations and exacerbations of chronic obstructive pulmonary disease.
abstract: BACKGROUND
  Increased bacterial concentration (load) in the lower airways and new bacterial strain acquisition have been posited as mechanisms for chronic obstructive pulmonary disease (COPD) exacerbations. Bacterial concentrations are higher during exacerbation than during stable disease; however, these studies are cross sectional and devoid of strain typing.
  
  
  OBJECTIVE
  To determine if the increased bacterial concentrations function as a separate mechanism for exacerbation induction independent of new strain acquisition.
  
  
  METHODS
  In a prospective, longitudinal cohort of patients with COPD, the relationship between exacerbation occurrence, sputum bacterial concentrations, and new strain acquisition was examined.
  
  
  RESULTS
  Clinical information, quantitative sputum cultures, and molecular typing of potential bacterial pathogen isolates. Over 81 months, 104 subjects completed 3,009 clinic visits, 560 (19.6%) during exacerbations and 2,449 (80.4%) during stable disease. Among preexisting strains, sputum concentrations of Nontypeable Haemophilus influenzae and Haemophilus haemolyticus were not different in exacerbation versus stable disease. Moraxella catarrhalis (stable, 10(8.38 +/- 0.13) [mean +/- SEM] vs. exacerbation, 10(7.78 +/- 0.26); p = 0.02) and Streptococcus pneumoniae (stable, 10(8.42 +/- 0.21) vs. exacerbation, 10(7.76 +/- 0.52); p = 0.07) concentrations were lower during exacerbations compared with stable periods. Concentrations of new strains of H. influenzae (stable, 10(7.28 +/- 0.15) vs. exacerbation, 10(7.76 +/- 0.17); p = 0.04) and M. catarrhalis (stable, 10(7.85 +/- 0.15) vs. exacerbation, 10(8.37 +/- 0.14); p = 0.02), were increased during exacerbations; however, the differences were small.
  
  
  CONCLUSIONS
  Change in bacterial load is unlikely to be an important mechanism for exacerbations. Better understanding of the host-pathogen interaction, rather than enumerating bacteria in respiratory samples, is required to provide new insights into bacterial infection in COPD.
authors.affiliation: Veterans Affairs Western New York Healthcare System (151), 3495 Bailey Avenue, Buffalo, NY 14215, USA. ssethi@buffalo.edu
authors.forename: Sanjay
authors.initials: S
authors.lastname: Sethi
authors.forename: Rohin
authors.initials: R
authors.lastname: Sethi
authors.forename: Karen
authors.initials: K
authors.lastname: Eschberger
authors.forename: Phyllis
authors.initials: P
authors.lastname: Lobbins
authors.forename: Xueya
authors.initials: X
authors.lastname: Cai
authors.forename: Brydon J B
authors.initials: BJ
authors.lastname: Grant
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Murphy
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015169:Colony Count, Microbial; D005260:Female; D006190:Haemophilus / Q000302:isolation & purification; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D001936:Moraxella catarrhalis / Q000302:isolation & purification; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D013183:Sputum / Q000382:microbiology*; D013296:Streptococcus pneumoniae / Q000302:isolation & purification