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Kefang Lai, MD, PhD; Ruchong Chen, MD, PhD; Nanshan Zhong, MD
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From the State Key Laboratory of Respiratory Diseases, Guangzhou Institute of Respiratory Diseases, The First Affiliated Hospital of Guangzhou Medical University.

Correspondence to: Nanshan Zhong, MD, FCCP, State Key Laboratory of Respiratory Diseases, Guangzhou Institute of Respiratory Diseases, The First Affiliated Hospital of Guangzhou Medical University, 151 Yanjiang Rd, Guangzhou, Guangdong, 510120, China; e-mail: nanshan@vip.163.com


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2013;144(1):363-364. doi:10.1378/chest.13-0924
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To the Editor:

We thank Dr Mao and colleagues for their interest and comments regarding our recent article in CHEST.1

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%).2 Another study in Hong Kong also showed that exposure to particulate matter in different geographic locations was associated with increased odds of having cough.3 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,4 and sulfur dioxide exposure increases cough response and airway inflammation in guinea pigs.5 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.

References

Lai K, Chen R, Lin J, et al. A prospective, multicenter survey on causes of chronic cough in China. Chest. 2013;143(3):613-620. [CrossRef] [PubMed]
 
Pan G, Zhang S, Feng Y, et al. Air pollution and children’s respiratory symptoms in six cities of Northern China. Respir Med. 2010;104(12):1903-1911. [CrossRef] [PubMed]
 
Lai 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(3):219-230. [CrossRef] [PubMed]
 
Anderson 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(1):47-56. [CrossRef]
 
McLeod 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(6):750-757. [CrossRef] [PubMed]
 

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References

Lai K, Chen R, Lin J, et al. A prospective, multicenter survey on causes of chronic cough in China. Chest. 2013;143(3):613-620. [CrossRef] [PubMed]
 
Pan G, Zhang S, Feng Y, et al. Air pollution and children’s respiratory symptoms in six cities of Northern China. Respir Med. 2010;104(12):1903-1911. [CrossRef] [PubMed]
 
Lai 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(3):219-230. [CrossRef] [PubMed]
 
Anderson 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(1):47-56. [CrossRef]
 
McLeod 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(6):750-757. [CrossRef] [PubMed]
 
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