title: Defining Chronic Cough: A Systematic Review of the Epidemiological Literature.
abstract: OBJECTIVE
  Recent evidence suggests a global burden of chronic cough in general populations. However, the definitions vary greatly among epidemiological studies, and none have been validated for clinical relevance. We aimed to examine previous epidemiological definitions in detail and explore the operational characteristics.
  
  
  METHODS
  A systematic review was conducted for epidemiological surveys that reported the prevalence of chronic cough in general adult populations during the years 1980 to 2013. A literature search was performed on Pubmed and Embase without language restriction. Epidemiological definitions for chronic cough were classified according to their components, such as cutoff duration. Meta-analyses were performed for the male-to-female ratio of chronic cough prevalence to explore operational characteristics of epidemiological definitions.
  
  
  RESULTS
  A total of 70 studies were included in the systematic review. The most common epidemiological definition was identified as 'cough ≥3 months' duration without specification of phlegm (n=50); however, it conflicted with the cutoff duration in current clinical guidelines (cough ≥8 weeks). Meta-analyses were performed for the male-to-female ratio of chronic cough among 28 studies that reported sex-specific prevalence using the most common definition. The pooled male-to-female odds ratio was 1.26 (95% confidence interval 0.92-1.73) with significant heterogeneity (I²=96%, P<0.001), which was in contrast to clinical observations of female predominance from specialist clinics. Subgroup analyses did not reverse the ratio or reduce the heterogeneity.
  
  
  CONCLUSIONS
  This study identified major issues in defining chronic cough in future epidemiological studies. The conflict between epidemiological and clinical diagnostic criteria needs to be resolved. The unexpected difference in the gender predominance between the community and clinics warrants further studies. Clinical validation of the existing definition is required.
authors.affiliation: Division of Allergy and Clinical Immunology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Woo Jung
authors.initials: WJ
authors.lastname: Song
authors.affiliation: Division of Allergy and Clinical Immunology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.|Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Yoon Seok
authors.initials: YS
authors.lastname: Chang
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, Castle Hill Hospital, University of Hull, Cottingham, East Yorkshire, United Kingdom.
authors.forename: Shoaib
authors.initials: S
authors.lastname: Faruqi
authors.affiliation: Division of Allergy and Clinical Immunology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Min Koo
authors.initials: MK
authors.lastname: Kang
authors.affiliation: Division of Allergy and Clinical Immunology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Ju Young
authors.initials: JY
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Chungbuk National University College of Medicine, Cheongju, Korea.
authors.forename: Min Gyu
authors.initials: MG
authors.lastname: Kang
authors.affiliation: Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Sujeong
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Pusan National University College of Medicine, Busan, Korea.
authors.forename: Eun Jung
authors.initials: EJ
authors.lastname: Jo
authors.affiliation: Department of Internal Medicine, Pusan National University College of Medicine, Busan, Korea.
authors.forename: Seung Eun
authors.initials: SE
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Ewha Woman's University School of Medicine, Seoul, Korea.
authors.forename: Min Hye
authors.initials: MH
authors.lastname: Kim
authors.affiliation: Department of Pathophysiology and Simulation Centre, Jessenius Faculty of Medicine, Comenius University, Martin, Slovak Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Plevkova
authors.affiliation: Division of Allergy and Clinical Immunology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Heung Woo
authors.initials: HW
authors.lastname: Park
authors.affiliation: Division of Allergy and Clinical Immunology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea. shcho@snu.ac.kr.
authors.forename: Sang Heon
authors.initials: SH
authors.lastname: Cho
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, Castle Hill Hospital, University of Hull, Cottingham, East Yorkshire, United Kingdom. a.h.morice@hull.ac.uk.
authors.forename: Alyn H
authors.initials: AH
authors.lastname: Morice
keywords: Cough; definition; epidemiology