Introduction There is considerable interest surrounding the role of chronic mucus hypersecretion (CMH) in the development of COPD but varying definitions of CMH have created uncertainty regarding its prevalence. Some studies characterise CMH as chronic phlegm production whilst others as chronic cough (CC) productive of phlegm. By understanding how these symptom groups relate to each other, we may be better equipped to interpret existing data and search for therapeutic targets. We report the prevalence and overlap of CMH and CC over 43 years of adult life from age 20 years within the nationally representative MRC National Survey of Health and Development (NSHD) birth cohort.
Methods The MRC NSHD is a birth cohort study of men and women born during one week in March 1946 within England, Scotland and Wales. CMH and CC presence was determined by completion of the MRC questionnaire on respiratory symptoms in the following years (study member age in years): 1966(20), 1971(25), 1982(36), 1989(43), 1999(53) and 2009(63). The MRC questionnaire defines CMH as the production of phlegm from the chest on most days for three months of each year and defines CC as cough on most days for three months of each year.
Results 1394 subjects (47% male) completed questionnaires on all six occasions between 1966 and 2009. 398 study members (26.8%) reported either symptom at least once with a majority of CMH reporters concurrently reporting CC (See Table 1). The percentage of CMH reporters concurrently reporting CC increased with age (0.5%/year increase, CI 0.18–0.82, p = 0.001).
Conclusion Most chronic phlegm producers report concurrent CC, and this percentage increases with age. Restricting CMH definition to those with CC, however, misses the substantial proportion of the population who report chronic phlegm production without CC. The requirement for a chronic cough to define CMH may underestimate the total prevalence of chronic sputum producers and hence those potentially at risk of COPD development or progression.