title: Changes in prevalence and load of airway bacteria using quantitative PCR in stable and exacerbated COPD.
abstract: BACKGROUND
  Prevalence and load of airway bacteria in stable and exacerbated chronic obstructive pulmonary disease (COPD) has been previously studied using microbiological culture. Molecular techniques, such as quantitative PCR (qPCR), may be more informative.
  
  
  METHODS
  In this study, 373 sputum samples from 134 COPD outpatients were assessed for prevalence and load of typical airway bacteria (Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis) by multiplex qPCR, with 176 samples analysed for atypical bacteria. Paired stable and exacerbation typical bacteria data were compared in 52 patients. We compared routine culture with qPCR in 177/373 samples.
  
  
  RESULTS
  Typical bacteria were more prevalent in exacerbation than stable-state paired samples: 30/52 (57.7%) vs. 14/52 (26.9%); p=0.001. In patients who were bacteria-positive at both time points, mean (±1 SEM) load was significantly higher at exacerbation than stable state (108.5(±0.3) vs. 107.2(±0.5) cfu/ml), constituting a 20-fold increase (p=0.011). qPCR was more discriminatory at detecting typical bacteria than microbiological culture (prevalence 59.3% vs. 24.3%; p<0.001). At stable state, higher airway bacterial load correlated with more severe airflow limitation (FEV(1)%predicted) (r=-0.299; p=0.033) and higher inhaled corticosteroid dosage (r=0.382; p=0.008). Mean C-reactive protein was higher in bacterial-associated exacerbations (35.0 Vs 25.1 mg/L; p=0.032).
  
  
  CONCLUSIONS
  Airway bacterial prevalence and load increase at COPD exacerbations and are an aetiological factor. qPCR is more discriminatory than culture, identifying higher airway bacterial prevalence. Exacerbations associated with bacterial detection showed a higher mean C-reactive protein level. In the stable state, airway bacterial load is related to more severe airflow limitation and higher inhaled corticosteroid dosage used.
authors.affiliation: Centre for Respiratory Medicine, University College London, London, UK. davinder.garcha.09@ucl.ac.uk
authors.forename: Davinder S
authors.initials: DS
authors.lastname: Garcha
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Thurston
authors.forename: Anant R C
authors.initials: AR
authors.lastname: Patel
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Mackay
authors.forename: James J P
authors.initials: JJ
authors.lastname: Goldring
authors.forename: Gavin C
authors.initials: GC
authors.lastname: Donaldson
authors.forename: Timothy D
authors.initials: TD
authors.lastname: McHugh
authors.forename: Jadwiga A
authors.initials: JA
authors.lastname: Wedzicha
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D005260:Female; D006193:Haemophilus influenzae / Q000302:isolation & purification*; D006801:Humans; D016014:Linear Models; D008131:London; D008297:Male; D001936:Moraxella catarrhalis / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000379:methods*; D015995:Prevalence; D029424:Pulmonary Disease, Chronic Obstructive / Q000382:microbiology* / Q000503:physiopathology*; D012129:Respiratory Function Tests; D013183:Sputum / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000302:isolation & purification*