PCR based bronchoscopic detection of common respiratory pathogens in chronic cough: a case control study

Peter W West,Angela Kelsall,Jaclyn A Smith,Samantha Decalmer,Paul W Bishop,Ashley A Woodcock,Winifred Dove,James P Stewart

doi:10.1186/1745-9974-8-5

Abstract

BackgroundViral respiratory tract infection is the most frequent cause of acute cough and is reported at onset in about one third of patients with chronic cough. Persistent infection is therefore one possible explanation for the cough reflex hypersensitivity and pulmonary inflammation reported in chronic cough patients.MethodsBronchoscopic endobronchial biopsies and bronchoalveolar lavage cell counts were obtained from ten healthy volunteers and twenty treatment resistant chronic cough patients (10 selected for lavage lymphocytosis). A screen for known respiratory pathogens was performed on biopsy tissue. Chronic cough patients also underwent cough reflex sensitivity testing using citric acid.ResultsThere was no significant difference in incidence of infection between healthy volunteers and chronic cough patients (p = 0.115) or non-lymphocytic and lymphocytic groups (p = 0.404). BAL cell percentages were not significantly different between healthy volunteers and chronic cough patients without lymphocytosis. Lymphocytic patients however had a significantly raised percentage of lymphocytes (p < 0.01), neutrophils (p < 0.05), eosinophils (p < 0.05) and decreased macrophages (p < 0.001) verses healthy volunteers. There was no significant difference in the cough reflex sensitivity between non-lymphocytic and lymphocytic patients (p = 0.536).ConclusionsThis study indicates latent infection in the lung is unlikely to play an important role in chronic cough, but a role for undetected or undetectable pathogens in either the lung or a distal site could not be ruled out.Trials registrationCurrent Controlled Trials ISRCTN62337037 & ISRCTN40147207

Highlights

Viral respiratory tract infection is the most frequent cause of acute cough and is reported at onset in about one third of patients with chronic cough
It is well known that viral infection of the upper respiratory tract is the most common cause of acute cough [2] and an increase in cough reflex sensitivity has been demonstrated during upper respiratory tract infections (URTI) in healthy subjects, similar to that seen in patients with chronic cough [3,4]
Through parallel comparison of chronic cough patients, sampled and tested in the same way as healthy volunteers, we have not been able to show an association between the presence of infection and lymphocytosis or cough reflex sensitivity

Summary

Introduction

Viral respiratory tract infection is the most frequent cause of acute cough and is reported at onset in about one third of patients with chronic cough. Persistent infection is one possible explanation for the cough reflex hypersensitivity and pulmonary inflammation reported in chronic cough patients. About one third of chronic cough patients recall an URTI at the onset of their cough, in one series 34% [9] and in our clinic approximately 30% (unpublished data). This suggests, that whilst the vast majority of URTI are self-limiting, some may persist to cause a troublesome chronic cough [10]. Largely unknown, factors may be driving cough hypersensitivity and the associated inflammation

Methods

Results

Conclusion