Chronic, intermittent productive cough linked to poor lung function trajectories
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Key takeaways:
- Poor lung function trajectories were found among those with chronic productive cough and those with intermittent productive cough.
- At age 53 years, cough and asthma prevalence were high in these individuals.
Both a chronic productive cough and an intermittent productive cough were linked to poor lung function trajectories spanning from childhood to adulthood, according to study results published in The Lancet Respiratory Medicine.
“People with nonchronic productive cough may require further medication attention,” Jingwen Zhang, MPH, of the allergy and lung health unit in the Centre for Epidemiology and Biostatistics at The University of Melbourne, told Healio.
“We would recommend clinicians, especially general practitioners, to consider measuring spirometry for people with productive cough, whether the cough is intermittent or persistent,” Zhang continued. “The presence of phlegm may not be helpful in terms of finding the cause of cough but could indicate underlying lung function impairment, which is often overlooked.”
Using data from the Tasmanian Longitudinal Health Study, Zhang and colleagues assessed 3,609 individuals (mean age, 53 years) who attended 10-year follow-up visits from a mean age of 7 years to 53 years and completed a self-reported cough questionnaire to determine how different cough subclasses impact lung function trajectories.
Researchers included nine questions related to coughing in the questionnaire to separate current coughers from non-coughers. Responding no to all these questions meant the individual was a non-cougher (n = 1,396), whereas responding yes to one or more of these questions meant the individual was a current cougher (n = 2,213; 51.9% female). Only current coughers moved forward in this analysis.
Cough subclasses, productive cough types
Within the cohort of current coughers, researchers classified each individual into one of six subclasses based on cough symptoms.
“We identified ‘novel’ cough subclasses,” Zhang told Healio, calling the method a “fundamentally different way of classifying cough.”
Over half of the cohort had cough with colds only (n = 1,189; 53.7%), and a smaller percentage of individuals had cough with allergies (n = 305; 13.8%), intermittent productive cough (n = 213; 9.6%), minimal cough (n = 206; 9.3%), chronic productive cough (n = 153; 6.9%) and chronic dry cough (n = 147; 6.6%).
Notably, individuals with the lowest probabilities of all symptoms belonged to the minimal cough subclass.
From age 7 years to age 13 years in the current cougher cohort, researchers observed a 10.6% drop in the overall prevalence of current productive cough. At age 13 years and beyond, individuals with chronic productive cough, intermittent productive cough and cough with allergies belonged to the groups with the most individuals with this type of cough.
Out of all six subclasses, ever chronic productive cough appeared the most frequently at all ages in individuals with chronic productive cough.
Lung function trajectories, asthma, smoking
Over the course of follow-up visits from age 7 years to 53 years, researchers found more individuals with FEV1 persistent low trajectories in the chronic productive cough (16.1%) and intermittent productive cough (6.4%) subclasses vs. the minimal cough subclass (2.9%).
Assessment of FEV1/FVC early low-rapid decline trajectories also showed that a greater proportion of individuals with chronic productive cough and intermittent productive cough had this trajectory than individuals with minimal cough (12.1% vs. 13% vs. 2.9%). This pattern was further found when looking at the number of individuals with a FEV1 trajectory of early below average, accelerated decline (9.7% vs. 14.2% vs. 1.5%).
In terms of symptoms, a greater proportion of individuals from the chronic productive cough (32.4%) and intermittent productive cough (50.3%) groups had cough at age 53 years when compared with the minimal cough group (0%).
Asthma also appeared in more individuals with chronic productive cough (26.9%) and intermittent productive cough (41.7%) at age 53 years vs. individuals with minimal cough (6.3%).
Between the six subclasses, researchers found that the cough with allergies subclass more often had trajectories for late-onset asthma and allergies, and the chronic productive cough subclass had trajectories for early-onset asthma and allergies.
In terms of smoking, the largest percentage of smokers at ages 30 to 53 years was observed in the chronic productive cough subclass despite a decline seen in the number of individuals reporting smoking and second-hand smoking as the years progressed.
At all assessed ages, second-hand smoking was reported the most in those with chronic productive cough and those with intermittent productive cough.
“Contrary to the current way of classifying cough by its duration, we unexpectedly found that the absence/presence of phlegm is equally if not more important as indicators of respiratory health,” Zhang told Healio. “People who have had chronic or intermittent productive cough (cough with phlegm) in their mid-50s had impaired lung function, increased respiratory symptoms (eg, cough, asthma, allergies) and high exposures to smoking (active and passive) since an early age (ie, 7 years).”
In contrast, individuals with a cough that lacked phlegm did not have these characteristics.
“Such features were not observed for people who had chronic dry cough as they seemed to be healthy until their mid-40s to 50s, much closer to the onset of their dry cough, even though their cough lasts longer than the intermittent productive cough subclass,” Zhang said.
Before concluding the study, researchers evaluated the six cough subclasses against standard definitions of cough and found similarities between the chronic productive cough subclass and the chronic bronchitis definition; the chronic dry cough subclass and the chronic cough definition; the chronic productive cough subclass and the chronic cough definition; and the minimal cough subclass and the non-cougher group.
“Cough patients seen from cough clinics can be very different from people with cough in the community,” Zhang told Healio. “Therefore, our results may be surprising and differ from clinical observations. However, our study provides unique data from the population level to understand the broad spectrum of cough and its relations to different risk factors (and treatment options).”
The cough subclasses identified in the study may be of use in future research, Zhang said.
“Future studies may use these refined cough definitions to identify risk factors, preventative measures and eventually treatment specific to different cough subclasses,” Zhang told Healio. “In addition to chronic cough, non-chronic cough with phlegm production may also require further research to understand this group of patients.”