Chronic productive cough is associated with death in smokers with early COPD

Abstract

Cough and phlegm are common in COPD. Previous studies have shown conflicting evidence regarding their association with mortality and lung function. We sought to better understand how cough and phlegm impact mortality and lung function in COPD. We analyzed data from the Lung Health Study, consisting of 5,887 smokers with mild to moderate airflow obstruction followed longitudinally. We assessed the association between baseline symptoms of cough alone, phlegm alone, and cough and phlegm with 12.5-year mortality and annual lung function decline. Average age at entry was 48.5 years (± 6.8) with 63% males and 4% African Americans. Cough alone was present in 17%, phlegm alone in 12%, while 31% had both. Neither symptom alone was associated with death, but the combination was associated with increased risk of death after adjustment for age, gender, race, smoking status at year 5, pack-years smoked, randomization group, baseline FEV1 percent predicted (HR 1.27, 95% CI 1.02-1.59). Individuals with cough and phlegm together more commonly died of respiratory causes than those without. Cough with phlegm was associated with 48 mL lower baseline FEV1 (95% CI -90, -6), while neither symptom alone was associated with baseline FEV1. No symptom was associated with FEV1 longitudinally. Cough and phlegm together are associated with mortality and lung function decrement in mild-to-moderate COPD, independent of lung function and smoking status. Respiratory causes of death are common among those with cough and phlegm. Such information can help to identify subsets of individuals with COPD having higher risk for adverse outcomes.

Keywords: Symptoms; lung function.; subtypes; survival.

Figure 1

Overlap of symptoms of cough and phlegm in the cohort. The Venn diagram depicts the overlap of symptoms of “usual cough” and “usual phlegm” in the cohort. All four symptom groups with proportion of individuals included in group depicted. (See methods section for definitions of “usual cough” and “usual phlegm”).

Figure 2

Proportion of individuals in four symptom groups reporting lower respiratory infection in the previous year in the baseline questionnaire. Lower respiratory infection included report of chest colds, bronchitis, pneumonia and flu.

Figure 3

Associations between individual symptoms and mortality over 12 years. Analyses were adjusted for age, gender, race, smoking status at year 5, baseline FEV₁ % predicted, pack-years smoked and randomization group. Group without cough or phlegm was the comparison group for all analyses of cough and phlegm. Points are hazard ratios and lines are 95% confidence intervals.