Changes in prevalence and load of airway bacteria using quantitative PCR in stable and exacerbated COPD

• Published in: Thorax Vol. 67; no. 12; pp. 1075 - 1080
• Main Authors: Garcha, Davinder S, Thurston, Sarah J, Patel, Anant R C, Mackay, Alexander J, Goldring, James J P, Donaldson, Gavin C, McHugh, Timothy D, Wedzicha, Jadwiga A
• Format: Journal Article
• Language: English
• Published: London BMJ Publishing Group Ltd and British Thoracic Society 01.12.2012; BMJ Publishing Group; BMJ Publishing Group LTD
• Subjects: Aged; Analysis of Variance; Bacteria; bacterial load; Batch processing; Biological and medical sciences; Cardiology. Vascular system; Chi-Square Distribution; Chronic obstructive pulmonary disease; Chronic obstructive pulmonary disease, asthma; colonisation; COPD; Dyspnea; exacerbations; Female; Haemophilus influenzae; Haemophilus influenzae - isolation & purification; Humans; Inflammation; Linear Models; London; Male; Medical sciences; Moraxella catarrhalis; Moraxella catarrhalis - isolation & purification; Mortality; Pneumology; Polymerase Chain Reaction - methods; Prevalence; Proteins; Pulmonary Disease, Chronic Obstructive - microbiology; Pulmonary Disease, Chronic Obstructive - physiopathology; quantitative PCR; Respiratory Function Tests; Sputum - microbiology; Staphylococcus infections; Steroids; Streptococcus pneumoniae; Streptococcus pneumoniae - isolation & purification; London; United Kingdom > UK; Lung disease; Load; Prevalence; Respiratory disease; Change; Polymerase chain reaction; Respiratory tract; Chronic; Bronchus disease; Anesthesia; Bacteria; Chronic obstructive pulmonary disease; Circulatory system; Obstructive pulmonary disease; Molecular biology; Cardiology; Quantitative analysis
• ISSN: 0040-6376; 1468-3296; 1468-3296
• DOI: 10.1136/thoraxjnl-2012-201924

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 (FEV1%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.