We believe that this is amongst the first studies to report validation of ATS respiratory questionnaire in a local language (Sindhi) in rural setting of Pakistan. The study shows that respiratory symptoms of cough, phlegm, wheeze and shortness of breath are significantly correlated with reduced lung function and this trend was found consistently for all lung volumes (FVC, FEV1 and FEV1/FVC). This correlation suggests that the presence of respiratory symptoms is an important predictor of impaired lung function and use of standardized respiratory questionnaires like ATS questionnaire therefore is an effective tool in estimating the burden of respiratory symptoms in a rural community setting. This finding has important Public Health implications for resource limited settings because use of such standardized questionnaires can serve as a cost saving tool in the diagnosis of respiratory symptoms without need of additional resources.
This study has reported significant association of all symptoms with both obstructive and restrictive lung patterns. These findings are similar to those reported in other studies. A number of studies conducted on different occupational groups have shown association of selective symptoms with reduced lung function. In one study symptoms of cough and phlegm were found to be significantly associated with obstructive pattern as opposed to wheeze or phlegm . While the predominant associations of selective symptoms with lung function changes reported in these studies can be attributed to specific occupational exposures, symptoms identified by questionnaires successfully predicted the impaired lung function which was verified by spirometry.
We collected the data on major confounders and adjusted the results in final analysis. The study area from where the sample was selected has high arsenic concentration in ground water. Studies have reported important role of arsenic in reduced lung function . We measured the levels of arsenic in drinking water sources which were adjusted in final results. Adjustment was also done for smoking, type of fuel used for cooking and type of kitchen which are independent factors of respiratory illnesses.
In this study, we also report the prevalence of physician diagnosed and self-reported asthma as 5.5% and 9.5% respectively. There is paucity of representative data regarding prevalence of asthma in Pakistan. Few studies that were conducted have estimated the burden of asthma among selective groups of population including children [23, 24] and some occupational groups  whereas our study estimated the burden of asthma in general population of adults. Prevalence reported in this study is somewhat similar to that reported using similar definition by WHO for Pakistan and neighboring countries like India, Bangladesh and Srilanka where it ranged between 2.6% to 3.16% . Possible reasons for variation in asthma prevalence in different studies could include the variation in operational definition of asthma amongst different studies. Use of definition such as physician diagnosed asthma may be appropriate in developed countries; however, asthma prevalence estimated on the basis of this definition can vary greatly in developing countries depending on availability of and access to health care facilities and required medicines . Random sampling error may be an alternate explanation for variation in prevalence in this study compared to the other studies. Our study population was exposed to arsenic through underground drinking water and prolonged exposure to arsenic is being increasingly recognized to affect the lung function [12, 27] however, further research is warranted to explore such associations. Although our study reports the prevalence of asthma from a localized community setting of a rural area, we believe that these estimates may be generalizable to similar rural settings in Pakistan especially along the river Indus since similar risk factors for respiratory illnesses are prevalent in these areas.
In addition to arsenic exposure, several other factors could be related to the presence of respiratory symptoms and asthma among this study population especially the use of biomass fuel for cooking and the type of kitchen being used. However, this study was not powered to detect the risk factors associated with respiratory symptoms due to limited sample size.
This study has few limitations that need to be considered. Due to cross sectional nature of the study, it is difficult to establish causal association between impaired lung function and the respiratory symptoms. Nevertheless, the consistent trend of decrement in lung volumes is of importance and provides basis for further research. This was a pilot study with a small sample size however, as a preliminary research, this study significantly adds to the scarcely available evidence regarding ATS respiratory questionnaire validation in rural community settings especially in the developing countries. We used spirometry as an objective measure of lung function to compare with the respiratory questionnaire. Spirometry has an added advantage of identifying impaired lung function among those who do not have manifest symptoms and it may not be possible to capture such impairment by use of questionnaire alone, as indicated by the results of our study, that show low sensitivity and positive predictive values while high specificity and negative predictive values for all the frequent or less severe as well as chronic or more severe symptoms in the ATS questionnaire. This finding is consistent with studies using different questionnaires that have also reported low sensitivity and high specificity .
There is scarce literature regarding comparison of ATS questionnaire with other respiratory questionnaires although available studies have reported analogous results. Asthma related items of ATS questionnaire have been compared with those of Medical research council questionnaire (MRC) and National Heart and Lung Institute questionnaire (NHLI) yielding similar responses . Therefore we believe that ATS questionnaire is a valid tool for assessment of respiratory symptoms in rural community settings.