Air Pollution and Chronic Cough in China: Response

Abstract

We thank Dr Mao and colleagues for their interest and comments regarding our recent article in CHEST.1Lai K Chen R Lin J et al.A prospective, multicenter survey on causes of chronic cough in China.Chest. 2013; 143: 613-620Abstract Full Text Full Text PDF PubMed Scopus (127) Google Scholar We agree that air pollution may be associated with cough. In a survey performed in six cities of northeastern China with heavy industrial air pollution, it was found that three air pollutants (total suspended particulates, SO2, NO2) significantly increased the prevalence of persistent cough in children (approximately 21%-28%).2Pan G Zhang S Feng Y et al.Air pollution and children's respiratory symptoms in six cities of Northern China.Respir Med. 2010; 104: 1903-1911Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar Another study in Hong Kong also showed that exposure to particulate matter in different geographic locations was associated with increased odds of having cough.3Lai HK Ho SY Wong CM Mak KK Lo WS Lam TH Exposure to particulate air pollution at different living locations and respiratory symptoms in Hong Kong—an application of satellite information.Int J Environ Health Res. 2010; 20: 219-230Crossref PubMed Scopus (13) Google Scholar It is reasonable to suppose that haze induces respiratory symptoms including cough. Air pollution is a common problem in China and is usually more serious in winter and spring. Therefore, the prevalence of cough may vary in different seasons because of air pollution, low temperature, and fireworks as mentioned by Dr Mao. However, our study was focused on the spectrum of causes of chronic cough in the specialist outpatient clinic but not the prevalence of chronic cough in the community. It is difficult to make a subgroup adjusted for air quality data across various regions to clarify its relationship with chronic cough in current cohort groups. A community survey with larger samples is needed in the future to confirm whether there are seasonal or regional differences on the prevalence of chronic cough related to air pollution in China. Dr Mao pointed out that haze should be the main cause of unexplained cough. In some patients with chronic cough, no cause is identified, leading to the diagnosis of idiopathic cough or unexplained cough, which is often associated with an increased response to tussive agents such as capsaicin. Common cold or influenza are often triggers of chronic cough (including the common causes and unexplained cough) in our experience. It is reported that air pollution exposure clearly exacerbates preexisting bronchial asthma,4Anderson HR Favarato G Atkinson RW Long-term exposure to air pollution and the incidence of asthma: meta-analysis of cohort studies.Air Qual Atmos Health. 2013; 6: 47-56Crossref Scopus (163) Google Scholar and sulfur dioxide exposure increases cough response and airway inflammation in guinea pigs.5McLeod RL Jia Y McHugh NA et al.Sulfur-dioxide exposure increases TRPV1-mediated responses in nodose ganglia cells and augments cough in guinea pigs.Pulm Pharmacol Ther. 2007; 20: 750-757Crossref PubMed Scopus (26) Google Scholar However, there is no study to identify that air pollutants are able to cause chronic cough or increase cough sensitivity in humans directly so far. As pointed out in our article, it is still unclear whether unexplained cough represents a single entity or includes certain undiscovered causes of chronic cough. We consider that air pollutants may contribute to persistent cough, but it is unknown whether haze is a main cause of the unexplained cough. As we addressed in the article, although there was variation on the frequency of certain single causes in different regions, the four common causes were consistent across five different regions in China. In summary, we suppose that air pollution (in particular, heavy pollution in mid to east China) as a cause of chronic cough should be further elicited. Air Pollution and Chronic Cough in ChinaCHESTVol. 144Issue 1PreviewIn a recent issue of CHEST (March 2013), Lai et al1 demonstrated that cough variant asthma, upper airway cough syndrome, eosinophilic bronchitis, and atopic cough (AC) constituted the main causes of chronic cough across five regions in China, based on a prospective survey using a modified diagnostic algorithm. They also concluded that geography, seasonality, age, and sex were not related to the spectrum of chronic cough. We do agree with the authors' viewpoint. However, of note, in developing countries like China one major concern with the environmental factors (haze) should be raised because indoor and outdoor pollutants can cause chronic cough; namely, exposure to pollutants, such as diesel exhaust, sulfur oxides, ozone, nitrogen oxides, and particulate matter, participates in the development of respiratory symptoms. Full-Text PDF