Introduction

Chronic respiratory diseases contribute 10.9% of the total deaths in India, of which chronic obstructive respiratory diseases (COPD) and asthma contribute 8.7% and 1.9%, respectively [1]. Of the total global DALYs (Disability adjusted life years), 3.9% was due to chronic respiratory diseases, of which India alone contributes 32% [2]. There are several occupational exposures that are known to cause respiratory morbidity and mortality [3]. Cement dust is a common and well known harmful exposure among individuals involved in manufacturing of cement and/or engaged at construction sites. The respirable crystalline silica particles in cement dust are the main reason for lung damage [4]. Observational studies have shown lower lung functions (Forced Vital Capacity (FVC): –200 ml to –1200 ml; Forced Expiratory Volume in 1second (FEV1): –300 ml to –800 ml; Peak Expiratory Flow Rate (PEFR) –1 L/s to –2.5 L/s [5, 6, 7, 8, 9, 10, 11, 12] and higher respiratory morbidity among factory workers with chronic exposure to cement dust compared to those less exposed or not exposed [5, 7, 8, 9, 11, 12, 13, 14].

In India, cement factories are registered under the 1948 Factories Act that ensures safety and health of the workers in formal sectors [15]. It is well known that 92% of employment in India is contributed by informal workers and that they are not under any safety act [16]. Notably, there is a significant contribution by the informal sector in the journey of cement from factories to the site of construction. There are currently no data documenting the lung function status or respiratory morbidity among informal workers chronically exposed to cement. Most informal workers are immigrants from poorer neighboring states and they have the highest proportion of extreme poverty compared to self-employed or salaried households (18% versus 7%) [16]. This vulnerable population is generally not included in formal population-based surveys or factory-based studies, which may lead to underestimation of the overall burden of respiratory illnesses that is attributed to occupational exposures [17].

Thus, a cross-sectional study was conducted among informal cement workers in the national capital, Delhi. The objectives of this study were, (1) to compare the lung functions of informal workers exposed to cement dust with those not exposed to cement dust, (2) to compare the prevalence of self-reported respiratory symptoms between the exposed and unexposed groups.

Methods

This was a comparative cross-sectional study and we followed Strengthening the Reporting of Observational studies in Epidemiology (STROBE) guidelines to report our findings [18].

Results

Two hundred participants provided information on socio-demography, lifestyle, and respiratory morbidity, of which 189 could provide valid spirometry readings (Figure 1). When compared to the combined (indoor and outdoor) unexposed group, exposed participants were older (40 years vs. 31 years), the majority were from a Muslim community (71% vs. 57%), literacy levels were low (43% vs. 79%), participants were living in kuccha houses (97% vs. 2%), and they had lower mean SES scores (3.18 vs. 4.26). Table 1 provides further information on demographic profile categorized by the three study groups.

Respiratory Symptoms

All respiratory symptoms, including cough, phlegm, breathlessness, wheezing, and chest illness were higher in the exposed group. Of the exposed participants, 86% had “any respiratory symptoms” compared to only 50% in unexposed groups. Half (50%) of the exposed group had “any high-grade symptoms” against only 20% in unexposed groups (Figure 2 and Figure S1). The odds of having “any respiratory symptoms” were significantly higher in the exposed group compared to the indoor unexposed group (OR = 7.38, 95%CI = 3.21 to 17.0) (Table 3) and the outdoor unexposed (OR = 5.34, 95%CI = 2.27 to 12.59) groups (Table S2). Similarly, the odds of experiencing “any high-grade respiratory symptoms” were significantly higher in the cement-exposed group compared to the indoor unexposed (OR = 3.46, 95%CI = 1.49 to 8.00) (Table 3) and the outdoor unexposed (OR = 3.07, 95%CI = 1.30 to 7.24) group (Table S2). Respiratory symptom scores were significantly higher in the exposure group (rate ratio (RR) = 2.45, 95%CI = 1.63 to 3.69) (Table 3) compared to the indoor unexposed (RR = 2.21, 95%CI = 1.48 to 3.31) (Table S2) and outdoor unexposed groups. Respiratory symptom scores were negatively correlated with lung function (Pearson’s coefficient FEV1/FVC = –0.37, FEV1 = –0.30, FVC = –0.18), with higher respiratory symptoms indicating poorer lung function.

Figure 2 

Prevalence of Respiratory Symptoms in the Three Study Groups.

Discussion

The higher burden of respiratory morbidity has been reported previously in workers exposed to cement dust but none of the studies earlier evaluated the respiratory health of informal workers exposed to cement dust. Informal workers exposed to cement in the present study had statistically significant lower lung function and higher respiratory symptoms when compared to unexposed informal workers. Informal workers engaged in outdoor work (not involving cement) had the best lung function when compared indoor unexposed and outdoor exposed groups. However, respiratory symptoms were least prevalent in indoor un-exposed informal workers. Increasing age was a significant factor in reduction of lung function across groups. To our knowledge this is the first study in India to report association of cement dust exposure with lung functions and respiratory morbidity among informal workers.

The control groups in the present study were chosen from contiguous geographical locations and somewhat similar sociodemographic characteristics. Since the exposed group was exposed to cement dust, environmental exposures, and engagement in strenuous physical labor, having an outdoor and indoor control group helped to adjust for environmental exposure as well as levels of physical activity, both of which have effects on lung function [22, 23]. The concordance between self-reported respiratory symptoms and an objectively measured lung function (r=-0.37) is a proof of validity of the self-reported symptoms reported in this study. However, our study has certain limitations. Firstly, the ambient air pollution was not measured, and the occupation was considered as a proxy for exposure. Secondly, our sample was based on convenient sampling, which could have led to underestimation of respiratory symptoms and overestimation of lung function (selection bias and healthy worker effect). Thirdly, the symptoms recorded were self-reported symptoms, which may be affected by reporting bias, leading to over-reporting in the exposed and under-reporting in the unexposed groups. Fourthly, we did not measure post-bronchodilator lung function that would have helped in diagnosing COPD. Finally, this was a cross-sectional design hence causal associations cannot be established.

There were no studies available globally that measured lung function and respiratory morbidity among informal workers exposed to cement dust. Hence, we compared our study findings with studies performed among cement factory workers conducted in Sub-Saharan Africa (n = 9 studies), Middle East (n = 6), Europe (n = 3), and Asia (n = 3). None were reported from India. The choice of control groups, variables used of adjusted analyses, and the questionnaire used for capturing respiratory questionnaire were varied across studies. Some studies chose apparently healthy controls outside factory settings [7, 10, 24] and some within factory settings but with less exposure [5, 6, 8, 9, 11, 12, 13, 14, 24, 25, 26]. All of these studies (Table 4) showed a significantly lower lung function and higher respiratory symptoms in factory workers exposed to cement dust compared to controls, and the magnitude of difference varied depending upon the choice of control group and whether or not these differences were adjusted for confounders (Table 4). Studies that used healthy controls outside factory settings had demonstrated larger differences than studies with controls from the same setting but with lower exposure. A further two studies had used multiple controls similar to ours [12, 26]. Choice of controls is an important design strategy to adjust for confounders.

The mean lung function parameters in our exposed group were lower than the previously reported studies except for one, which reported a mean of FVC, FEV1, and PEF of 1.59L, 1.54L, and 4.04 L/s, respectively (Table S1) [7]. Similarly, the proportion with respiratory symptoms like cough, phlegm, breathlessness, and wheezing were higher (71%, 58%, 51%, and 35%) in our sample than previously reported. Based on this external comparison, we can hypothesize that informal workers were having a higher burden of respiratory illness compared to formal workers exposed to cement. This larger deficit among exposed informal workers could be due to underlying malnutrition and poor living conditions. However, a comparative study between formal and informal workers exposed to cement within Indian context is required to confirm this finding.

In this study we detected a difference in FVC that was smaller (small effect) than the differences in PEFR (moderate effect), and this could reflect the overall poorer lung capacity of informal workers across groups but with a higher level of obstructive air flow disease among the exposed workers. This could be an important finding that could inform the sample size calculation of future comparative studies.

Different questionnaires were used in previously reported studies to measure self-reported symptoms [5, 7, 8, 14]. The most commonly used respiratory symptom questionnaires was from The British Medical Research Council (BMRC). Other questionnaires were those from the International Union against Tuberculosis and Lung Disease (IUATLD), the National Program of Silicosis Control, Iran, the Thai Thoracic Society, and The American Thoracic Society (ATS 1978). Irrespective of the questionnaire used, the prevalence of respiratory symptoms was higher when compared to the control groups. The proportion with cough varied from 15% to 70%, phlegm 15% to 45%, breathlessness 4% to 55%, and wheezing 5% to 67% among the exposed group, which was similar to the 69%, 50%, 58%, and 35%, respectively, observed in our study. However, none reported a summary score of any symptoms and high-grade symptoms.

Our study findings are important, as informal workers are often ignored in surveys and regulatory acts that safeguard the rights and safety of workers. In India, since a large percentage (92%) of workers are involved in informal employment [16], these populations are vulnerable in several ways; they are usually migrant workers with no social security cover, poor access to health care, and not covered under the Factories Act. They are daily wage earners by default and only the fittest continue to work. Hence, documenting the ill effects of hazardous occupations is crucial to obtain unbiased estimates of the burden of risk factors and health outcomes. Further amendment of existing policies related to workplace safety that cover informal workers are urgently required. Policy changes should make employers of contractual laborers responsible for worker’s safety, such as provision of protective gear to the exposed workers and making its use mandatory.

To conclude, our study demonstrated that informal workers exposed to cement dust showed poorer respiratory health when compared to those who are not exposed to cement dust. Impactful public health policies inclusive of informal workers are urgently needed to protect India’s workforce.

Additional File

The additional file for this article can be found as follows: