Defining Chronic Cough: A Systematic Review of the Epidemiological Literature

PURPOSE: 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 > or =3 months' duration without specification of phlegm (n=50); however, it conflicted with the cutoff duration in current clinical guidelines (cough > or =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.

Chronic cough in subjects with upper airway diseases

Cough is the commonest respiratory symptom leading to a medical consultation. Although acute cough which is usually associated with respiratory viral infection is not a problem to manage, chronic cough is frequently a diagnostic and therapeutic challenge as it does not respond to usual treatments. Specific group of chronic coughers are considered to have upper airway diseases, lately categorized as having upper airway cough syndrome. There is an increasing pool of evidence that upper airway diseases have significant involvements in the regulation of cough reflex, indicating that they must be taken into considerations as major triggers of coughing in the patients. Here we summarize current literature and experiences on the pathogenesis of upper airway cough syndrome, and discuss further clinical applications.