Caging the coughing canary in the global lung health coal mine

Coughing is an explosive violent act. It is surprisingly common, and when it becomes chronic, it is a real nuisance causing considerable distress. And now, in the midst of a respiratory pandemic, people with chronic cough feel ‘judged’ and may feel stigmatized as a result of a difficult to control symptom. It is against this background that in a recent publication in Respirology, Zhang and colleagues1 have a careful look at the risk factors for chronic cough. Knowing what puts you at risk might give some clues on how to manage this intractable problem. They use a systematic review and meta-analysis methodology to evaluate the relevant literature. The studies look at chronic cough in the general population, which is not the same as a clinic population, but does give a broad perspective on the issue. Their fig. 1 is a particularly useful summary of the article. It not only reports risk factors, but also indicates possible protective factors for chronic cough. Here, we learn that reducing air pollution levels and certain dietary patterns are protective for chronic cough. Surely, this provides even more strength to the arguments for adopting a lifestyle that is healthy for your lungs: a healthy lung lifestyle, let us do it!

When looking at risks for chronic cough, these fall into three key domains: diseases, lifestyle exposures and the social determinants of health. We see environmental exposures and common diseases emerging as important and potentially controllable issues. Smoking is a known and preventable risk factor that requires persistent and ongoing vigilance. Inhaling PM10 particles from outdoor air pollution is a risk factor that is in the spotlight at present, being generated by bushfires and the burning of fossil fuels. Reducing PM10 levels is good for both the global health of the planet and for our lung health. An early signal of benefit might be a reduction in cough due to this cause.

The observation that asthma is associated with a three-fold increased odds of chronic cough confirms clinical observations. Airway hyperresponsiveness, but not atopy, is associated with cough risk, giving some mechanistic insights that suggest it is physiological airway dysfunction rather than allergy that confers the cough risk. What are the implications for asthma? The current focus of asthma care targets symptom control, but cough is not part of the asthma control assessment. This means that a potentially treatable disease component might not be addressed. This omission is partly historical, as the commonly used assessment of asthma control was designed to assess the top five symptoms, and when the questionnaire/tool was developed, cough was number 6, and just missed out.2 Fortunately, newer approaches to asthma, such as treatable traits, recognize the importance of cough and include cough hypersensitivity as a treatable trait.3, 4 We now have positive clinical trials showing treatment pathways for this problem using both pharmacological and non-pharmacological interventions.5

There is a third area of risk that is sort of known but is seldom addressed in clinical settings. In the domain of the social determinants of disease, we learn that low socioeconomic status/low education level and certain occupations are risk factors for chronic cough. These are areas that can be identified by targeted clinical history.

You would think that by knowing the risk factors for a clinical problem you could then successfully target therapy. But when you look at each of the risk domains that have been identified, that is asthma, exposures and the social determinants of health, they are areas where success is limited. It is not so much therapeutic nihilism but rather therapeutic impotence. There are clear opportunities for new approaches, such as addressing cough in the context of lung health, utilizing the treatable traits approach to manage asthma and getting inventive and radical when it comes to managing the social determinants of health. But where to start? In this article, Zhang and colleagues gives us the risk factors for cough that we can attach to the lung health flag. This can be used to direct attention to caging the coughing canary in the global lung health coal mine.

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