Introduction Airway bacterial infections are associated with COPD exacerbations. The most frequently identified bacteria in COPD are Haemophilus influenzae (HI), Moraxella catarrhalis (MC) and Streptococcus pneumoniae (SP) (Wilkinson et al, 2006), though studies have used culture techniques, with little data available on PCR methodology in airway infection. Using the London COPD cohort, we aimed to assess and quantify bacterial prevalence and load via quantitative PCR, in paired baseline and exacerbation sputum samples.
Methods Quantitative PCR was utilised, measuring prevalence and load on paired baseline and exacerbation samples, with baseline samples obtained within 1 year prior to its paired exacerbation. SP, HI and MC gene targets were Spn9082; Haemophilus influenzae P4 lipoprotein gene; copB outer-membrane-protein gene, respectively. The baseline state was defined as being at least 6 weeks after, and 2 weeks before, an exacerbation. Exacerbation was defined as two consecutive days of at least two increased symptoms (Anthonisen criteria), at least one of which is a major symptom (dyspnoea; sputum purulence; sputum volume).
Results Sixty-nine paired baseline and exacerbation sputum samples were obtained from 56 patients: mean (±SD) age 71.0 years (±8.4); predicted FEV1 46.4% (±17.0); male gender 60.4%; current smoker 30.2%. Bacteria were detected at significantly higher rate at exacerbation, being seen in 36/69 (52.2%) exacerbations, and 19/69 (27.5%) baseline samples (χ2-test; p=0.003). Mean bacterial load was significantly higher at exacerbation, with mean load of 8.3 (±1.1) log10 cfu/ml, compared with mean of 7.3 (±1.8) log10 cfu/ml at baseline (paired-samples t test; p<0.001), indicating a 10-fold overall-load increase at exacerbation. MC frequency increased significantly from 4.3% (3/69) at baseline to 17.4% (12/69) at exacerbation (p=0.014). Prevalence of HI (17.4% vs 26.1%) and SP (8.7% vs 20.3%) showed non-significant increases. Mean loads of SP and MC increased significantly from baseline to exacerbation (p=0.048; p=0.008, respectively).
Conclusion Prevalence and load of airway bacteria in COPD increases from baseline to exacerbation. This confirms that bacteria play an important role in exacerbation aetiology, implicating increasing bacterial load as a key underlying mechanism, and emphasises the importance of prompt antibiotic therapy at COPD exacerbation.