Bacteria and sputum inflammatory cell counts; a COPD cohort analysis
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RESEARCH
Bacteria and sputum inflammatory cell counts; a COPD cohort analysis Augusta S. Beech1,2* , Simon Lea1, Umme Kolsum1, Zhang Wang3, Bruce E. Miller4, Gavin C. Donaldson5, Jadwiga A. Wedzicha5, Christopher E. Brightling6 and Dave Singh1,2
Abstract Background: There is evidence that bacterial colonisation in chronic obstructive pulmonary disease (COPD) is associated with increased neutrophilic airway inflammation. This study tested the hypothesis that different bacterial phyla and species cause different inflammatory profiles in COPD patients. Methods: Sputum was analysed by quantitative polymerase chain reaction (qPCR) to quantify bacterial load and 16S rRNA gene sequencing to identify taxonomic composition. Sputum differential cell counts (DCC) and blood DCC were obtained at baseline and 6 months. Patients were categorised into five groups based on bacterial load defined by genome copies/ml of ≥ 1 × 104, no colonisation and colonisation by Haemophilus influenzae (H. influenzae), Moraxella catarrhalis (M. catarrhalis), Streptococcus pneumoniae (S. pneumoniae), or > 1 potentially pathogenic microorganism (PPM). Results: We observed an increase in sputum neutrophil (%), blood neutrophil (%) and neutrophil–lymphocyte ratio (NLR) in patients colonised with H. influenzae (82.6, 67.1, and 3.29 respectively) compared to those without PPM colonisation at baseline (69.5, 63.51 and 2.56 respectively) (p 1PPM group consisted of patients with colonisation of two or three PPMs; 92% were colonised with H. influenzae, with 58% colonised with H. influenzae + S. pneumoniae, while 42% showed evidence of M. catarrhalis colonisation and 8.3% were colonised with all three bacterial species (for details see Additional file 1, Table S1). The total number of patients in the entire cohort with M. catarrhalis colonisation was 19 (8.1%). There was no difference in bacterial colonisation in frequent exacerbators (≥ 2 exacerbations in the previous year) compared to non-frequent exacerbators (Additional file 1, Table S2), or in patients using ICS compared to those not using ICS (data not shown). Sputum cell counts
145 patients with qPCR data had sputum DCCs available; induced samples were more cellular based on total cell count (× 106/g), with total neutrophil and macrophage counts (× 106/g) also higher in induced samples in the subset with this information available (n = 112). However, in the total sample (n = 143) with available DCCs, the sputum cell percentages between induced
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Table 1 Baseline demographics of patients enrolled onto this study Characteristic
n = 236
Gender (% male)
74
Age
69.5 (8.3)
Smoking status (current %)
34
Pack years
47.5 [10–220]
BMI (kg/m2)
26.3 [17.3–47.0]
Exacerbations (1 year period)
1 [0–15]
Post FEV1 (L)
1.5 (0.6)
Post FEV1 (%)
57.4 (18.5)
CAT
18 (7.5)
SGRQ-C (total)
47.0 (18.2)
GOLD
2 [1–4]
1 (%)
12.0
2 (%)
52.1
3 (%)
29.1
4 (%)
6.8
LABA only (%)
2.5
LAMA only (%)
5.5
ICS only (%)
1.7
ICS + LABA (%)
13.1
ICS + LAMA (%)
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