Repeated virus identification in the airways of patients with mild and severe asthma during prospective follow-up

Background: Respiratory viruses may persist in the airways of asthmatics between episodes of clinical worsening. We hypothesized that patients with clinically stable, severe asthma exhibit increased and more prolonged viral presence in the airways as compared to mild asthmatics and healthy controls. Methods: Thirty-five subjects (no cold symptoms > 4 weeks) entered a 12-week prospective study using three groups: clinically stable mild asthma (GINA 2) (n = 12, age 34.1 +/- 13.4 year), severe asthma (GINA 4) (n = 12, age 49.3 +/- 14.8 year) and healthy controls (n = 11, age 37.9 +/- 14.2 year). All subjects underwent spirometry and completed a written questionnaire on asthma symptoms at baseline. Nasal and throat swabs, induced sputum samples, exhaled breath condensate and gelatine-filtered expired air were analysed at 0, 6 and 12 weeks by a multiplex real-time PCR assay for 14 respiratory viruses using adequate positive and negative controls. Results: Thirty-two of 525 patient assessments (6%) showed a virus-positive sample. Among the 14 respiratory viruses examined, HRV, adenovirus, respiratory syncytial virus, parainfluenza 3&4, human bocavirus, influenza B and coronavirus were detected. When combining all sampling methods, on average 18% of controls and 30% of mild and severe asthmatics were virus positive, which was not different between the groups (P = 0.34). The longitudinal data showed a changing rather than persistent viral presence over time. Conclusion: Patients with clinically stable asthma and healthy controls have similar detection rates of respiratory viruses in samples from nasopharynx, sputum and exhaled air. This indicates that viral presence in the airways of stable (severe) asthmatics varies over time rather than being persistent.