Abstract
Background: Respiratory syncytial virus (RSV) is increasingly recognized as an important pathogen in adults with cardiopulmonary disease. It has been associated with acute exacerbations of chronic obstructive pulmonary disease (COPD); however, it has also been detected in the lower airway in the stable state, but the consequences of RSV in stable disease have not previously been determined. We therefore studied the consequences of RSV persistence in adults with COPD and its effect on airway inflammation and lung function decline.
Methods: A total of 241 sputum samples from 74 patients with COPD (FEV1% predicted, 39.2%; interquartile range, 29.6–57.8%) were collected quarterly in the stable state over 2 yr. RSV was detected by polymerase chain reaction (PCR), quantitative microbiology was performed, and inflammatory cytokines were quantified by ELISA.
Results: RSV RNA was detected in 32.8% of sputum samples. Patients in whom RSV was more frequently detected (> 50% of samples RSV PCR-positive, n = 18) had higher airway inflammation and faster FEV1 decline over the study (101.4 ml/yr [95% confidence interval, 57.1–145.8]) compared with those with less frequent detection of RSV (n = 56; 51.2 ml/yr [31.7–70.8]; p = 0.01). The observed relationship between RSV detection and accelerated lung function decline was independent of smoking status, exacerbation frequency, and lower airway bacterial load.
Conclusions: Persistent RSV detection in patients with COPD is associated with airway inflammation and accelerated decline in FEV1. Chronic RSV infection may be a novel therapeutic target to alter the natural history of COPD.
Chronic obstructive pulmonary disease (COPD) is a major and growing cause of ill health and death worldwide. The Global Burden of Disease Study predicts that it will rise to being the third commonest cause of death by 2020 (1). Although cigarette smoking is the major cause, evidence exists that chronic lung infection may sustain inflammation in the small airways and lung parenchyma, leading to accelerated and progressive loss of lung function characteristic of COPD (2–4). There is some evidence that chronic airway infection with adenovirus may play a role in the development of airway obstruction, but studies have been cross-sectional in nature and relationships between viral infection and disease progression have not been demonstrated (5). Furthermore, a role for RNA viruses in the pathogenesis of COPD has been little explored.
Respiratory syncytial virus (RSV) is a negative-strand RNA virus of the Pararmyxoviridae family, genus Pneumovirus, and is the major cause of acute lower respiratory tract infections in young children, where it occurs in winter epidemics but is rarely identified in the summer (6, 7). Human RSV has no animal reservoir and the source of these winter epidemics remains unknown. Recent studies have also identified RSV as an important pathogen in the elderly (8–10) and in adults with cardiopulmonary disease (8, 11).
We have previously detected RSV in nasopharyngeal samples from patients with COPD in a cross-sectional study (12). Although the other commonly detected respiratory viral pathogens, such as human rhinovirus, were much more prevalent at exacerbation than in the stable state, RSV was detected at similar rates regardless of whether the patient was stable or having an exacerbation (12). Using quantitative polymerase chain reaction (PCR), these findings have been confirmed in patients with stable COPD and at exacerbation, with low viral loads identified in comparison to those seen in children with seasonal bronchiolitis (13). However, longitudinal studies to determine whether RSV is able to persist in the lower airways of patients with stable COPD are lacking and the clinical consequences of RSV persistence have not been determined.
We therefore prospectively studied a cohort of patients with well-characterized COPD with repetitive sampling in the stable state to determine the nature of RSV persistence in the lower airway. We investigated the effects of RSV persistence on lung function decline and airway inflammation and investigated interactions with lower airway bacterial colonization. Some results of this study have previously been reported in the form of abstracts (14, 15).
Patients with COPD were recruited from outpatient clinics into our COPD cohort. Ethics approval for the study was obtained from the East London and City Health Authority Research Ethics committee; all patients gave written, informed consent. The inclusion criteria for this study have previously been published (2, 12, 16–20) and include FEV1 of less than 70% predicted for age and height, β2-agonist reversibility of less than 15% of baseline and/or less than 200 ml, and an FEV1/FVC of less than 70%. Work from this cohort has been published in a number of previous studies (2, 4, 12, 16–20). Additional information is included in the online supplement.
At recruitment, patients were taught how to record post-bronchodilator PEF on diary cards each morning (Mini-Wright, Clement Clark International Ltd, Harlow, UK).
Patients were reviewed at recruitment and with their diary cards every 3 mo in the study clinic to monitor compliance with data collection, record changes in medication, and baseline lung function. Review of diary cards was used to ensure that stable sampling was performed, when subjects had been clear of exacerbation symptoms and had completed any exacerbation treatment for at least 6 wk.
Lung function was measured with a rolling seal spirometer (Sensor Medic Corp., Yorba Linda, CA). Lung function measurements were taken between 9:30 and 11:30 a.m., 1 h after the patient's usual bronchodilator medication. At least three spirometry readings were taken at each visit and the best performance recorded.
Sputum was sampled if the subject met criteria for the stable state at three monthly reviews. Additional detail on the sampling and processing methods is provided in the online supplement. An aliquot of phosphate-buffered saline–processed sputum was frozen at –80°C for subsequent RNA extraction. The remainder was analyzed for inflammatory cytokines using ELISA (2, 16, 19), sputum interleukin 6 (IL-6) and IL-8 (R&D Systems, Abingdon, UK) (2), and myeloperoxidase (MPO; EMD Biosciences, San Diego, CA).
Samples were processed by using sputolysin; serial dilutions were made and cultured on appropriate media. These were incubated for 18 h at 37°C in an atmosphere of air plus 5% CO2. After incubation, bacterial colonies were enumerated and subcultured for identification by standard methods (21). The number of colony forming units per gram of sputum was calculated from the total number of colonies obtained and the dilution to give the total bacterial count for each sample expressed in colony forming units per milliliter (cfu ml−1).
RNA extraction from the sputum was performed using a standard extraction kit (Qiagen, Crawley, UK). Reverse transcription was performed using random hexamers, and nested RSV virus PCR was performed as previously described (12) using taq polymerase. Positive and negative controls were run with all samples analyzed. A random sample of the PCR product from RSV-positive sputa was taken and both strands sequenced using a standard dye terminator method. These were compared with a reference RSV strain using Clone Manager (Scientific and Educational Software, Cary, NC) to align the sequences. Additional detail on the methods is provided in the online supplement.
Baseline recruitment data are presented as medians (interquartile ranges [IQRs]). The annual exacerbation frequency was calculated by dividing the total number of exacerbations per patient by the number of days the patient recorded data and multiplying by 365. Normally distributed data are reported by means (SD) and skewed data by medians (IQR). Appropriate comparative statistical tests were performed dependent on the distribution of the data.
We hypothesized that a greater frequency of detection of RSV in the stable airway is associated with greater inflammation and thus faster decline in lung function. Studies to date had been cross-sectional in nature and hence pilot data on the periodicity of RSV infection were not available; we therefore predetermined a cut-off limit of 50% detection rate to divide patients into high and low RSV groups. To analyze the effects of RSV colonization independently of patient characteristics (smoking status, exacerbation frequency, bacterial load, and starting FEV1) on decline in lung function, we used the general linear mixed model (xtreg) procedure in STATA-5 software (Stata Corporation, College Station, TX). These procedures are designed for panel (cohort) data and are particularly useful where data are correlated, as in repeated-measures designs and where there are complex error structures (4). We included as independent variables (a) time and (b) FEV1 measurement during the stable state, as two of four independent variables. The third variable was whether or not the patient was persistently colonized with RSV, which required 50% of their samples to be RSV positive. The fourth independent variable (d) was an interaction term obtained as the product of a and c. Allowance for confounders was made by including whether the patient had a bacterial load or inflammatory marker less or greater than the cohort median, exacerbation frequency greater or less than the cohort median, and active smoking status together with terms to adjust for the effect of these on FEV1 decline. Also included in the regression model was the starting FEV1 to adjust for differences in the rate of FEV1 decline between patients with high or low starting FEV1. The magnitude and significance of the effect of RSV colonization on decline were unchanged with inclusion of one or all of these confounders.
As multiple sputum samples were obtained during the study and the unit of analysis was the patient, the first sample obtained from each patient suitable for estimation of inflammatory cytokines was used in the analysis. p Values of 0.05 or less were regarded as significant.
Table 1 shows the baseline spirometric and other characteristics of 74 patients (45 male) who were sampled during the study. There were no differences between the baseline characteristics in terms of sex distribution, FEV1, FEV1% predicted, FVC, PEF, reversibility, years of smoking, current smoking status, exacerbation frequency of these patients and the 31 patients in the cohort who were not sequentially sampled (due to recruitment in the latter part of the study, use of long-term oral steroids, or intolerance of sputum induction). There were no significant differences in these variables between sputum producers and those requiring sputum induction. The 74 patients provided 241 stable sputum samples suitable for processing for analysis. Of these patients, 16 (of whom 8 died) of the 74 patients withdrew before the end of the study period. Diary card data were collected on a mean of 656 d/person (maximum possible in study, 762 d); compliance with data collection was thus 86%.
Sampled Patients (n = 74) | |||
|---|---|---|---|
| Median | IQR | ||
| Age, yr | 67.4 | 62.2–71.4 | |
| FEV1, L | 0.98 | 0.77–1.37 | |
| FEV1, % predicted | 39.2 | 29.6–57.8 | |
| FEV1, % reversibility | 7.94 | 0.8–13.1 | |
| FVC, L | 2.41 | 1.86–2.90 | |
| FEV1/FVC, % | 43.9 | 35.5–53.1 | |
| PEF, L/min | 158 | 122–238 | |
| PaO2, kPa | 8.94 | 8.14–9.43 | |
| PaCO2, kPa | 5.88 | 5.32–6.29 | |
| Smoking, yr | 45 | 39–51 | |
| Inhaled corticosteroid dose, mg/d* | 1000 | 500–2,000 | |
| Exacerbation frequency, per yr | 2.51 | 1.28–3.83 | |
Fifty-nine of the 74 patients sampled had RSV detected in at least one stable sputum sample during the study. Overall RSV was detected in the stable state in 32.8% of the 241 stable sputum samples collected. Sequencing of both strands of 10 randomly selected RSV-positive PCR samples confirmed homology in each case with RSV.
Of the samples, 36.8% of winter samples (December–February), 27.1% of spring samples (March–May), 36.7% of summer samples (June–August), and 34.0% of autumn samples (September–November) were RSV PCR positive. The incidence of RSV detection in stable patients showed no significant seasonality (p = 0.558). There was no difference in detection rates between spontaneous and induced sputum samples.
To study whether detection of RSV in sputum was due to persistence of the virus in particular individuals or merely as a result of sporadic infection, we compared the predicted probability of RSV detection occurring in all samples from an individual based on the overall detection rate of 32.8%, to the actual prevalence of patients with RSV throughout the study. The probability that an individual would have RSV in four of four sputum samples based on a random distribution of the virus in this population is 0.0116, or 1.16%; the actual prevalence of patients with RSV in four of four positive samples is 0.2, or 20%, suggesting persistence in certain individuals.
Patients were categorized a priori using their stable-sample RSV status in two groups: “low RSV” (in which ⩽ 50% of their samples were RSV PCR positive) and “high RSV” (in which > 50% of samples were positive). There were 18 patients in the high RSV group and 56 patients in the low RSV group. There was no difference in the number of available samples per patient between the two groups (p value = 0.424), or in baseline characteristics or the inhaled corticosteroid dosage between the two groups (see Table 2). Similarly, there were no differences in exacerbation frequency between the groups; 55% in the high RSV and 48% in the low RSV group were frequent exacerbations (with an annual rate of ⩾ the cohort median of 2.51 [IQR, 1.27–3.83]).
Low RSV Patients* (n = 56) | High RSV Patients* (n = 18) | ||||||
|---|---|---|---|---|---|---|---|
| Median | IQR | Median | IQR | P Value (Wilcoxon) | |||
| Age, yr | 67.4 | 61.7–71.8 | 68.7 | 62.2–71.7 | 0.748 | ||
| FEV1, L | 0.95 | 0.77–1.37 | 1.09 | 0.73–1.38 | 0.735 | ||
| FEV1, % predicted | 39.2 | 29.6–57.8 | 42.9 | 29.0–59.4 | 0.759 | ||
| FEV1, % reversibility | 9.1 | 2.1–13.1 | 3.70 | 0.0–12.8 | 0.231 | ||
| FVC, L | 2.37 | 1.68–2.90 | 2.60 | 2.00–3.28 | 0.297 | ||
| FEV1/FVC, % | 44.1 | 35.5–53.1 | 41.3 | 26.9–54.7 | 0.696 | ||
| PEF, L/min | 152 | 120–238 | 186 | 147–230 | 0.661 | ||
| PaO2, kPa | 9.00 | 8.13–9.62 | 8.47 | 8.27–9.22 | 0.387 | ||
| PaCO2, kPa | 5.91 | 5.32–6.31 | 5.81 | 5.32–6.11 | 0.713 | ||
| Smoking, yr | 46 | 37–52 | 42.5 | 39–50 | 0.555 | ||
| Inhaled corticosteroid dose, mg/d† | 1000 | 500–1,800 | 1000 | 600–2,000 | 0.600 | ||
| Exacerbation frequency, per yr | 2.40 | 1.32–3.87 | 2.76 | 1.04–3.37 | 0.821 | ||
| % | % | p Value χ2 | |||||
| Sex, males | 60 | 60.8 | 0.976 | ||||
| Chronic dyspnea | 44.8 | 52.7 | 0.780 | ||||
| Chronic wheeze | 34.3 | 32.4 | 0.211 | ||||
| Chronic cough | 41.0 | 37.8 | 0.506 | ||||
| Chronic sputum production | 41.8 | 27.8 | 0.988 | ||||
| History of smoking | 98.2 | 100.0 | 0.568 | ||||
| Smoking at recruitment | 41.8 | 27.8 | 0.288 | ||||
Between the first and last RSV samples, there were 781 FEV1 readings on the 74 patients, an average of 8.37 per patient. For those in whom RSV was detected in more than 50% of samples; the high RSV group (n = 18) showed a decline in FEV1 of 101.4 ml/yr (95% confidence interval [CI], 57.1–145.8) compared with 51.2 (31.7–70.8) ml/yr in the low RSV group (⩽ 50% samples were RSV PCR positive, n = 56). The difference in rate of FEV1 decline between these two groups was significant (p = 0.01; Figure 1).
Figure 1. Relationship between respiratory syncytial virus (RSV) detection pattern and FEV1 decline over study period. Heavy lines represent decline in FEV1 with standard errors (SEs) for (1) low RSV (⩽ 50% of sputum samples were RSV polymerase chain reaction [PCR] positive; n = 56; 51.2 ml/yr; SE, 10.1; confidence interval [CI], 31.7–70.8), intercept 0.97 (SE, 0.42; CI, 0.90–1.05; continuous lines), and (2) high RSV (> 50% sputum samples, RSV PCR positive; n = 18; 101.4 ml/yr; SE, 0.017; CI, 57.1–145.8), intercept 1.03 (SE, 0.08; CI, 0.88–1.19; dashed lines).
[More] [Minimize]Of the 56 patients in the low RSV group, 20 (35.7%) were active smokers, and of the 18 patients in the high RSV group, 4 (22.2%) were active smokers. If an adjustment for active smoking status was made in the analysis of the relationship between RSV detection and FEV1 decline, there remained a significantly faster decline in the high RSV group by an additional 47.9 ml/yr (0.8–87.8; p = 0.019). The effect of smoking itself on FEV1 decline was not significant (p = 0.205) in this analysis. In a covariate analysis adjusting for any effects of exacerbation frequency on differences in rate of FEV1 decline between RSV groups, there remained a faster decline in the high RSV group by 50.6 ml/yr (p = 0.013).
To ensure that variation in the number of samples obtained per patient did not affect the relationship between RSV detection and lung function decline, a subgroup analysis of patients with the same number of sputum samples was made using the sample number of four per patient. The relationship between RSV detection and FEV1 decline remained significant (p = 0.009), with a faster decline in FEV1 of 52.2 (CI, 13.3–91.3) ml/yr in the high RSV group subset.
Total bacterial load was available for 213 of the 241 samples. The overall prevalence of bacterial pathogens (PPMs) was 66.1%. The mean (SD) airway bacterial load was greater in the high RSV patients (108.12[0.48] log cfu/ml), compared with low RSV patients (107.76 [0.58]log cfu/ml; p = 0.024). There was no significant association between the detection of RSV and isolation of individual PPMs, or with all potential pathogenic organisms as a group (p > 0.17 in all cases).
Detection of RSV was associated with higher levels of airway inflammation as measured by sputum IL-6, IL-8, and MPO (p < 0.001 in all cases). The relationships between RSV detection category and airway inflammatory markers are shown in Figure 2.
Figure 2. Comparison of sputum interleukin 6 (IL-6; pg/ml), IL-8 (pg/ml), and myeloperoxidase levels (ng/ml) for low RSV and high RSV patient groups (p < 0.001, for difference between groups in all cases using cross-sectional regression analysis assuming a Poisson distribution in the dependent variable to allow for repeated measures). Sputum IL-6 (182 [178–185] and 253 [244–261] pg/ml), IL-8 (2,571 [2,558–2,585] and 3,229 [3,197–3,262] pg/ml), myeloperoxidase (10.3 [7.5–13.2] and 23.0 [16.7–29.3] ng/ml) for low RSV and high RSV patient groups, respectively.
[More] [Minimize]Levels of individual airway inflammatory markers above the median were associated with a trend to faster FEV1 decline. High levels of IL-6 were associated with additional FEV1 decline of 6.7 ml/yr (CI, 11.8–25.3), with high IL-8; 12.2 ml/yr (−6.4–30.9) and with high MPO 6.9 ml/yr (8.3–22.1), but these did not reach significance (p > 0.18 in all cases). To determine if the association between RSV detection and lung function decline was independent of airway inflammation, inflammatory markers were included in the model of analysis. The differences between FEV1 decline in high and low RSV groups were not statistically independent of associations with airway inflammation. Additional decline in high RSV group with IL-6 as a covariate: 42.9 ml/yr (−12.6–98.4, p = 0.13); for IL-8, 39.9 ml/yr (−16.0–95.9, p = 0.16); and for MPO, 28.0 ml/yr (−23.8–79.8, p = 0.29).
After allowance for total bacterial load, smoking status, and starting FEV1, high RSV patients had an FEV1 decline of 114.7 ml/yr (95% CI, 42.4–186.8) compared with the decline of 56.6 ml/yr (26.2–87.0) seen in low RSV patients (p < 0.05 for the difference between the two groups). If the FEV1 data were expressed as a percentage of the predicted FEV1, high RSV patients had a significantly faster decline of 1.94%/yr (0.2–3.63) in addition to the decline of 2.1%/yr (0.9–3.3) in low RSV patients (p = 0.03). If exacerbation frequency was included in the multivariate analysis, the faster decline in the high RSV group remained significant independent of any effects of exacerbations (19.3 [2.2–36.3] ml/yr, p = 0.027). A multivariate analysis with airway inflammation (MPO), smoking status, starting FEV1, bacterial load, and exacerbation frequency revealed a nonsignificant finding of an additional 6.9-ml/yr FEV1 decline (−15.4–29.2, p = 0.545) relative to the low RSV group.
This is the first longitudinal prospective study to investigate the role that RSV may play in the etiology and progression of stable COPD. We show that RSV RNA can be detected in the sputum of many patients with COPD in the stable state, and its detection is associated with higher levels of airway inflammation, greater airway bacterial loads, and an accelerated decline in lung function.
RSV is an established cause of acute respiratory illness in children, and RSV bronchiolitis is associated with the development of persistent wheeze in later childhood (22); however, it is not clear whether this association is causal. The role of viral infection in the etiology of airway obstruction in adults is even less well established. In a different setting, Retamales and colleagues reported that adenovirus E1A protein was expressed in respiratory epithelial cells in patients with emphysema, and that the quantity of E1A expression correlated with disease severity and inflammatory cell numbers (5). However, to date, longitudinal studies to determine the role of latent viral infection in COPD disease progression have been lacking. The data from this study suggest that RSV may play a role in the pathogenesis of airway inflammation and subsequent deterioration in lung function in adults with COPD.
Persistent RSV infection is well known in children with T-cell immunodeficiency, and has been demonstrated in the lungs of guinea pigs (23) and mice (24) for up to 150 d after experimental infection. In these animal models, RSV persistence was associated with continued infectivity and chronic airway inflammation despite an appropriate systemic humoral (23, 24) and T-cellular immune response (24).
In both acute and chronic models of infection, the key sites for RSV-induced inflammation in the lung are the small airways, in which epithelial damage and increased mucous production result in small airway obstruction and hyperinflation (25). It is of note that the small airways are also the primary site for the persisting inflammation and airway obstruction, which are characteristic of COPD (26, 27). Biopsies of subjects with COPD have demonstrated that the small airways are infiltrated with inflammatory cells, in particular CD8+ cells, neutrophils, and airway macrophages (27, 28). In particular, the presence of CD8+ T cells and B lymphocytes organizing into follicles was associated with disease progression (27). The findings of this study may suggest CD8+ T-cell populations, characteristic of COPD airway biopsies, may be recruited to the lung due to persistent viral infection, but an impaired immune response that is incapable of eliminating virus infection permits ongoing replication at low levels.
RSV detection was associated with heightened airway inflammation in terms of increased levels of IL-6, IL-8, and MPO. It is possible that RSV has direct proinflammatory effects on the airway, which may contribute to faster decline in lung function. The observed association between RSV detection and FEV1 decline remained significant if possible confounders such as airway bacterial load, exacerbation frequency, smoking status, and baseline FEV1 were included in the analysis. However, if airway inflammation was included in the covariate or multivariate model, no significant effect of RSV on lung function independent of airway inflammation was seen. One explanation is that RSV, inflammation, and decline are causally linked; however, it is also possible that inflammation predisposes the airway to viral persistence and that RSV detection is therefore an epiphenomenon. The direct relationship between airway inflammation and lung function decline was not significant in this analysis. This may be due to other noninflammatory processes such as airway remodeling (27) and effects on cellular apoptosis (29) or via other arms of the inflammatory cascade (30). However, over a longer follow-up period in a similar patient population, direct relationships between lung function decline and airway inflammation have been demonstrated (4), and therefore a similar relationship may have been found with prolongation of the follow-up period of this study. An alternative explanation of our findings is that patients with more aggressive COPD and faster disease progression have impaired acquired or innate immune responses, allowing RSV to persist. To determine the causal role of RSV infection, one would need to attempt to eradicate RSV with vaccines or antiviral drugs now under development.
Although RSV may have proinflammatory effects, it is also possible that it acts by modulating the response of lung cells to other inflammatory stimuli, including bacterial lipopolysaccharide (31), or by promoting neutrophil adhesion, thereby augmenting lung damage (32). Bacterial colonization of the lower airway in patients with COPD is well described (2, 3, 33, 34) and provides a stimulus to airway inflammation and disease progression (2). The additional presence of RSV in the lower airway may augment bacterially driven inflammation. It is also possible that chronic viral infection of the lower airway occurs due to increased susceptibility in individuals with existing bacterial colonization, although we found no direct association between the isolation of PPMs and detection of RSV. It is feasible therefore that eradication of airway bacteria may result in local repair and improvement of local defenses against viral persistence.
The relative importance of airway bacterial infection in COPD has been shown to increase with disease severity (34). This study was performed with a group of patients with moderate to severe disease and therefore the findings that RSV can be detected and is associated with accelerated disease progression in this population may not necessarily be extrapolated to patients with milder disease. Further studies across the full spectrum of disease as well as in smoking and nonsmoking control subjects are required to better understand the role of this pathogen in adults.
The use of sputum to detect the presence of RSV in the stable state allows repeated sampling of patients with advanced disease, which alternative techniques, such as bronchoscopic sampling, do not manage. The use of sputum sampling in a longitudinal cohort study inevitably results in a variable number of samples obtained per patient, and this problem is further compounded by the use of quality control in processing to exclude inadequate samples. However, this quality-control step is a vital one, because variations in sampling methodology are likely to be responsible for the differences in detection of RSV in patients with stable COPD seen in one study to the next (13, 35). Although PCR detection assays may appear, on paper, to be highly sensitive, it is apparent that the type of biological sample taken (sputum rather than swab), the rapidity of sample processing and storage, and the nucleic acid extraction techniques used all impact on the likelihood of detection of RSV RNA by PCR (35).
The use of highly sensitive PCR assays may detect viral nucleic acids; however, this does equate to detection of intact and pathogenic virus. Furthermore, our PCR technique did not distinguish between RSV type in this study and it is not known whether the virus isolated from an individual is genetically stable and representative of chronic infection rather than recurrent reinfection. Further studies are required to confirm the exact nature of viral persistence in the lower airway of patients with COPD.
This study did not examine the detection rates for RSV among normal control subjects, but the PCR detection techniques used in this study have also been used previously. In a number of these other studies, healthy control groups have been studied and low detection rates have been found. Indeed, we have studied adult control groups in two recent studies; the detection rates for RSV in both of these was zero (36, 37), suggesting that RSV detection in the stable state may be a factor in patients with moderate to severe COPD, but not in healthy control subjects.
In conclusion, we have shown that RSV RNA can be detected from lower airway samples of some patients with COPD in the stable state, with evidence of persistent detection in certain individuals. RSV RNA detection was associated with greater airway inflammation and accelerated disease progression in these patients. These findings suggest that RSV may play a role in the natural history of stable COPD. However, further investigation into the nature and consequences of viral persistence are required to confirm whether RSV is a potential therapeutic target in this important patient group.
The authors thank the following persons for their valuable assistance: Mike Edwards, John Hurst, Tata Kebadze, Simon Lloyd-Owen, Irem Patel, Wayomi Perera, Ray Sapsford, Terence Seemungal, Angela Whiley, and Mark Wilks.
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