title: Clinical and physiological features of postinfectious chronic cough associated with H1N1 infection.
abstract: BACKGROUND
  Post infectious chronic cough is a disabling illness. In 2009 an influenza pandemic occurred due to a novel strain of H1N1 influenza. Prolonged symptoms such as chronic cough remaining after the infection has cleared have not been examined. This study sought to investigate the prevalence, characteristics and mechanism of chronic cough following laboratory-confirmed H1N1 2009 influenza.
  
  
  METHODS
  Out of 836 eligible patients who had been tested by PCR assay for H1N1, 136 responders participated. Nineteen underwent detailed clinical investigation of cough, and airway function using symptom questionnaires, hypertonic saline challenge, and cough monitoring.
  
  
  RESULTS
  Post H1N1 chronic cough was reported by 43%, and chronic cough after non-H1N1 infection was present in 36% of participants. In the participants who progressed to testing objectively measured cough frequency was 3 times greater; there was a 9-fold increase in cough reflex sensitivity and greater quality of life impairment in the participants with postinfectious chronic cough following H1N1 infection than for the participants with no cough following H1N1 infection and for the healthy controls.
  
  
  CONCLUSIONS
  This study reports the first evaluation of chronic cough following H1N1 infection. Patients that develop chronic cough after H1N1 infection display increased cough reflex sensitivity up to 220 days after confirmed infection. There is an absence of associated risk factors and less impairment in quality of life compared to those patients normally seen in a specialist cough clinic. The associated mechanism was found to be cough reflex hypersensitivity.
  
  
  BACKGROUND
  This clinical trial has been registered with the Australian New Zealand Clinical Trials Register, ACTRN12610000540011.
authors: Priority Centre for Asthma and Respiratory Diseases, School of Medicine and Public Health, The University of Newcastle, Newcastle, 2308 NSW, Australia. Nicole.Ryan@newcastle.edu.au
authors: Nicole M
authors: NM
authors: Ryan
authors: Anne E
authors: AE
authors: Vertigan
authors: John
authors: J
authors: Ferguson
authors: Peter
authors: P
authors: Wark
authors: Peter G
authors: PG
authors: Gibson
mesh_terms: D000328:Adult; D001315:Australia; D002908:Chronic Disease; D002986:Clinical Trials as Topic; D003371:Cough / Q000821:virology*; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000150:complications / Q000276:immunology* / Q000503:physiopathology; D008297:Male; D060885:Multiplex Polymerase Chain Reaction / Q000379:methods*; D015995:Prevalence; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013997:Time Factors