title: A longitudinal assessment of acute cough.
abstract: BACKGROUND
  Cough can be assessed with visual analog scales (VAS), health status measures, and 24-hour cough frequency monitors (CF(24)). Evidence for their measurement properties in acute cough caused by upper respiratory tract infection (URTI) and longitudinal data is limited.
  
  
  OBJECTIVE
  To assess cough longitudinally in URTI with subjective and objective outcome measures and determine sample size for future studies.
  
  
  METHODS
  Thirty-three previously healthy subjects with URTI completed cough VAS, Leicester Cough Questionnaire (LCQ-acute), and CF(24) monitoring (Leicester Cough Monitor) on three occasions, 4 days apart. Changes in subjects' condition were assessed with a global rating of change questionnaire. The potential for baseline first-hour cough frequency (CF(1)), VAS, and LCQ to identify low CF(24) was assessed.
  
  
  RESULTS
  Mean ± SD duration of cough at visit 1 was 4.1 ± 2.5 days. Geometric mean ± log SD baseline CF(24) and median (interquartile range) cough bouts were high (14.9 ± 0.4 coughs/h and 85 [39-195] bouts/24 h). Health status was severely impaired. There was a significant reduction in CF(24) and VAS, and improvement in LCQ, from visits 1-3. At visit 3, CF(24) remained above normal limits in 52% of subjects. The smallest changes in CF(24), LCQ, and VAS that subjects perceived important were 54%, 2- and 17-mm change from baseline, respectively. The sample sizes required for parallel group studies to detect these changes are 27, 51, and 25 subjects per group, respectively. CF(1) (<20.5 coughs/h) was predictive of low CF(24).
  
  
  CONCLUSIONS
  CF(24), VAS, and LCQ are responsive outcome tools for the assessment of acute cough. The smallest change in cough frequency perceived important by subjects is 54%. The sample sizes required for future studies are modest and achievable.
authors.affiliation: Division of Asthma, Allergy and Lung Biology, Denmark Hill Campus, King's College London, London, United Kingdom.
authors.forename: Kai K
authors.initials: KK
authors.lastname: Lee
authors.forename: Sergio
authors.initials: S
authors.lastname: Matos
authors.forename: David H
authors.initials: DH
authors.lastname: Evans
authors.forename: Patrick
authors.initials: P
authors.lastname: White
authors.forename: Ian D
authors.initials: ID
authors.lastname: Pavord
authors.forename: Surinder S
authors.initials: SS
authors.lastname: Birring
mesh_terms: D000208:Acute Disease; D000328:Adult; D003371:Cough / Q000209:etiology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008991:Monitoring, Physiologic; D011788:Quality of Life; D012141:Respiratory Tract Infections / Q000150:complications*; D018401:Sample Size; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires