Global Respiratory Health

Chronic cough is a common respiratory symptom that affects the life of millions of people

Coughing on most days, without having a cold, for several months is one of the most common reasons why people book an appointment with their GP. Chronic cough is bothersome and has been linked to poorer health in people without obvious disease. However, the prevalence of – that is the proportion of people with – chronic cough and its associated risk factors are not well known in different regions of the world.

Using data from adults in the multinational Burden of Obstructive Lung Disease (BOLD) study, we estimated the prevalence of chronic cough in 41 locations from 34 countries around the globe and identified the factors that are more likely to determine the occurrence of chronic cough. We found a wide variation in the proportion of people with chronic cough across the different study locations – from 3% in Pune (India) to 24% in Lexington, KY (United States of America). Perhaps not surprisingly, tobacco smoking and working in a dusty job were the main risk factors for chronic cough. We identified other factors such as passive smoking, having had tuberculosis, being obese, having a low level of education and having hypertension.

Despite our findings, in many locations, we still cannot explain all of the prevalence of this chronic cough.

This manuscript has been published in eClinicalMedicine and is available here: doi.org/10.1016/j.eclinm.2024.102423. This work was conducted as part of the PhD thesis of Hazim Abozid.

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The BOLD study’s past and present

The Burden of Obstructive Lung Disease (BOLD) cohort is a large, multinational, prospective study of chronic respiratory disease. It started with the intention to measure the prevalence, risk factors, and impact of chronic obstructive pulmonary disease (COPD) in different populations around the world. COPD is a common and serious lung condition that causes breathing difficulties, coughing, wheezing, and reduced quality of life. It is estimated that COPD affects around 300 million people worldwide and is a leading cause of death globally.

The BOLD study has been a reference in the study of COPD because of its strengths:

• wide coverage of world regions and ethnic groups;

• large sample of representative population-based data;

• use of a standardised protocol, including the same questionnaires and same model of machine to test lung function, across study sites;

• centralised training and certification of interviewers and spirometry technicians. The quality of the data was monitored throughout the study, and re-training of staff was carried out if necessary;

• high quality of lung function measurements made before and after administration of a bronchodilator, with centralized quality control and assessment of all spirometry curves.

The BOLD cohort is still ongoing and will continue to provide important data and insights for the prevention, diagnosis, and management of COPD. More details about the past and present BOLD cohort can be found on the study’s website and in the profile published in the International Journal of Epidemiology (https://doi.org/10.1093/ije/dyad146).

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Respiratory symptoms are common among dust- and fume-exposed workers

It has been suggested that about 15 in 100 cases of chronic lung disease are caused by workplace exposures. These exposures can be anything from noxious gases, dust, which are very small dry airborne particles of biological or mineral origin, and fumes, such as those generated from welding. Most of the evidence that supports this estimate comes from wealthy countries in Europe and North America. Data on the association of lung disease with occupational exposures in other regions of the world are limited.

To improve the understanding of the relationship between occupational exposures and lung disease across the world, we used data from almost 29,000 adults, aged 40 and above, who participated in the Burden of Obstructive Lung Disease (BOLD) study. In this study, we asked participants about their job. We asked whether they worked in any of 11 settings considered to increase their exposure to dust or fumes. We also asked them whether they had a frequent cough, recurring mucous production, shortness of breath or wheezing. In addition, each of them had their lung function measured through spirometry.

We found that respiratory symptoms, that is frequent cough, recurring mucous production, shortness of breath and wheezing, were more common among people who worked in settings considered to have higher exposure to dusts and fumes. These findings were consistent across the several world regions. Interestingly and contrary to previous reports, we saw no evidence of a link between occupational exposures and worse lung function. At any rate, actions to avoid or reduce occupational exposures are still advised.

To learn more about this study check out the open-access peer-reviewed article in the European Respiratory Journal (https://doi.org/10.1183/13993003.00469-2022). This work was conducted as part of the PhD thesis of Jate Ratanachina.

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