We have read with great interest the article on the prevalence and determinants of COPD in Spain (EPISCAN II), which offers the best information on the epidemiology of the disease in our country.1 Two of the study's results stand out: the spirometrically-defined prevalence of COPD in Spain is 11.8%, and the underdiagnosis of the disease is 74.7%. The authors acknowledge that one of the limitations of the study is that it was conducted essentially in an urban setting. There is a significant lack of knowledge on the epidemiology of chronic respiratory diseases in general, and COPD in particular, in rural areas of our country. Studies carried out in the USA have found rural-urban disparities in the prevalence of COPD, which is higher in rural areas.2 The reason is likely to be multifactorial: tobacco use is higher and access to smoking cessation programs is limited in rural populations. Lower socioeconomic status could also be a risk factor for COPD in this population. Finally, environmental biomass smoke exposure is higher in this setting.2 This is a recognized risk factor for COPD, even in developed countries.3 Therefore, the global prevalence of COPD found in EPISCAN II might underestimate the disease burden in rural population.

Furthermore, it is plausible that underdiagnosis rates are higher in rural than in urban areas. Clinical guidelines strongly emphasize the association between tobacco smoke and COPD, and the diagnosis may be delayed in non-tobacco-related COPD. Future analyses of EPISCAN II will likely explore whether there is a relationship between smoking history and underdiagnosis of the disease. Access to spirometry may also be limited for rural residents, and this is another credible source of underdiagnosis in this setting. The On-Sint study, carried out in our country, revealed that being followed-up in a rural setting was associated with an inadequate diagnosis of COPD.4

Acquiring accurate information on the epidemiology of COPD in rural Spain becomes highly desirable in view of the results of a recently published study: while mortality attributable to chronic lower respiratory disease in urban areas of the USA is declining, it is increasing in rural areas, widening the rural-urban gap in mortality.5 This is in contrast to cardiovascular disease-related mortality, which is decreasing both in rural and urban areas.5 It is currently speculative if a similar trend could be found in mortality from COPD in Spain.

It is obvious that confirming possible differences in the prevalence, impact or underdiagnosis of COPD in rural areas would have policy implications, aimed at increasing support to improve prevention, diagnosis and treatment of the disease in this setting. Therefore, epidemiological studies focused specifically on this population are urgently needed, and should be promoted by the Spanish Society of Pulmonology and Thoracic Surgery (SEPAR).