Preplanned Studies: Prevalence and Types of Comorbidities in Pneumoconiosis — China, 2018–2021

Pneumoconiosis, an interstitial lung disease induced by dust exposure, represents a significant and prevalent occupational health hazard in China (1). Often, individuals with pneumoconiosis have experienced prolonged exposure to mineral dust, thus significantly impairing their respiratory system’s clearance and defense mechanisms. The chronic and progressive nature of pneumoconiosis remarkably compromises the patient’s immunity. Furthermore, pneumoconiosis patients frequently exhibit a range of comorbidities or complications, including pulmonary tuberculosis (PTB), non-tuberculosis (non-TB) lung infection, pneumothorax, chronic obstructive pulmonary disease (COPD), and chronic pulmonary heart disease. Patients are typically approaching 60 years of age, and the majority are middle-aged to elderly individuals. These patients might also endure additional chronic diseases, such as hypertension and diabetes, alongside pneumoconiosis. The concurrent manifestation of two or more of these aforementioned diseases or conditions within the same individual constitutes multimorbidity (2). Given the aging population and advancements in medical technology, the occurrence of multimorbidity is increasing. Consequently, managing individuals with multiple chronic diseases has emerged as a global challenge for societal and healthcare systems (3).

While some studies have examined the comorbidities associated with pneumoconiosis in specific locales or industries, a comprehensive, large-scale assessment of multimorbidity in pneumoconiosis patients throughout China is yet to be conducted. To address this gap, we performed a cross-sectional survey between December 2017 and June 2021 to understand the patient health statuses and the utilization of medical services by pneumoconiosis patients across 27 provincial-level administrative divisions (PLADs) in Chinese mainland — survey not including Tianjin Municipality, Shanghai Municipality, Hainan Province, and Xizang (Tibet) Autonomous Region.

Our survey employed a face-to-face questionnaire, administered by trained physicians and nurses specializing in occupational diseases. We collected a total of 11,181 valid responses and included 10,137 qualified pneumoconiosis patients in our analysis, amounting to 90.7% of all respondents. The respective annual breakdown of our analytical sample consisted of 953 (9.4%) in 2017, 2,077 (20.5%) in 2018, 3,529 (34.8%) in 2019, 3,084 (30.4%) in 2020, and 494 (4.9%) in 2021.

Using the survey data, we analyzed the distribution of the prevalence of 13 common comorbidities or conditions in pneumoconiosis patients. We stratified these distributions by gender, urban or rural residence, stage of pneumoconiosis, and smoking index. Furthermore, we calculated the prevalence rates, along with their 95% confidence intervals (CIs) for multimorbidity in various age groups, categorizing these by gender, residence, stages of pneumoconiosis, and smoking index. We also explored the patterns of multimorbidity stratified by urban and rural areas. These findings aim to inform the development of effective treatment strategies and health security policies for pneumoconiosis in China.

The questionnaire considered for this study assesses eleven self-reported chronic diseases. Participants were asked, “Have you been diagnosed with any of the following diseases or conditions during treatment or examination at hospitals or outpatient clinics: PTB, lung cancer or mesothelioma, diabetes, hypertension, pulmonary heart disease, cardiovascular diseases (CVDs), cerebrovascular diseases, non-TB lung infection, COPD, pulmonary bullae or pneumothorax, and rheumatism?” The remaining two conditions were determined from the participants’ body mass index (BMI), which included obesity (BMI≥24.0 kg/m²) and underweight (BMI<18.5 kg/m²). For the purposes of statistical analysis, age was categorized as follows: ≤44 years, 45–59 years, and ≥60 years. The smoking index was calculated by multiplying the number of cigarettes smoked daily by the years of smoking. Multimorbidity (MM1+) was defined as a patient having one or more of these 13 diseases or conditions within one pneumoconiosis patient population.

Data conforming to a normal distribution was articulated as mean±standard deviation (SD), while categorical data was represented by numbers (percentages). This study scrutinized the statistical significance of disparities using one-way analysis of variance (ANOVA) or t-tests for continuous variables of normal data distribution, assuming equal variances. For continuous variables exhibiting normal or nearly normal distribution, Pearson correlation analysis was utilized. For categorical data, Chi-square analysis and Fisher’s exact test were deployed. Linear-by-Linear Association (LLA) test was applied to calculate P-values for trends concerning proportions and prevalence. All statistical tests were two-sided, with P<0.05 indicating statistical significance. SPSS software (version 26.0, SPSS Inc., Chicago, IL, USA) was used to conduct all the aforementioned statistical analysis. Further information about the survey design, sample, subject background, questionnaire approaches, and data processes is outlined in a previous publication (4). This paper reports on the prevalence of 13 diseases or conditions in the subjects, with 11 being primarily self-reported by patients based on diagnostic results.

Ethical approval for this research was granted by the Ethics Committee of the National Institute for Occupational Health and Poison Control, associated with the Chinese Center for Disease Control and Prevention (Approval No. 201720). Written informed consent was obtained from all participants.

Of the 10,137 participants in the study, 97.4% were men (n=9,875) with an average age of 57.6 years (SD=11.5). This was notably younger than the female participants, who had an average age of 68.1 years (SD=13.7; F=211.067, P<0.001). Patients in urban locations were older than those in rural areas (F=969.257, P<0.001), and the age of participants decreased correspondingly with the stage of pneumoconiosis (F=159.243, P<0.001). Approximately 39.7% of the participants (n=4,021) were aged 60 years or older. Comparatively, the group aged 60 and above had a higher proportion of females than males (70.2% vs. 38.9%; χ²=104.970, P<0.001). It also had a higher proportion of urban rather than rural participants (53.3% vs. 29.1%; χ²=611.700, P<0.001). Significant statistical differences were observed in the proportions of middle-aged and elderly patients according to their varying clinical stages of pneumoconiosis and those without a stage (47.5% vs. 39.5% vs. 30.6% vs. 22.9%; χ²=303.048, P<0.001).

The prevalence rates for patients with one to six or more comorbidities were 28.8% (2,924/10,137), 15.9% (1,612/10,137), 10.6% (1,074/10,137), 5.9% (599/10,137), 2.9% (291/10,137), and 1.9% (189/10,137), respectively. Of these patients, 66.0% (95% CI: 65.1–66.9) had at least one comorbidity, and 37.1% (95% CI: 36.2–38.1) had two or more comorbid actions. Higher prevalence rates were found in male patients, urban residents, and patients with a smoking index of 200 or higher, with an increased rate coinciding with the severity of pneumoconiosis. Table 1 details the distribution of incidence and prevalence for 13 diseases or conditions, divided by gender, residential area, pneumoconiosis stage, and smoking index.

Table 1 reveals that respiratory and circulatory system diseases were the most common comorbidities. Women had higher prevalence rates of circulatory system diseases, COPD, obesity, and diabetes, while men had higher rates of pulmonary bullae or pneumothorax and arthritis. Urban patients had a higher prevalence of circulatory system diseases, pulmonary infection, COPD, obesity, and diabetes, whereas rural patients had higher rates of PTB, underweight, pulmonary bullae or pneumothorax, and arthritis. Stage I patients showed higher rates for obesity, diabetes, hypertension, CVDs, and cerebrovascular diseases, while stage III patients had higher rates for PTB, underweight, pulmonary bullae or pneumothorax, and other respiratory diseases. Individuals with a smoking index of ≥200 had higher rates of PTB, obesity, hypertension, cerebrovascular disease, COPD, pulmonary bullae or pneumothorax, and arthritis.

A positive correlation was found between the number of comorbidities and age (r=0.328, P<0.001). An increase in the prevalence of MM1+ with age was observed, landing at 54.3% (95% CI: 51.2–57.4), 58.4% (95% CI: 57.0–59.7), and 78.6% (95% CI: 77.3–79.8) for age groups ≤44 years, 45–59 years, and ≥60 years, respectively (χ²=419.135, P<0.001). Age-stratified analysis according to gender, locality, pneumoconiosis stage, and smoking index consistently demonstrated an increased prevalence with ascending age. MM1+ prevalence rates were notably elevated among female patients, urban dwellers, those in stage III of pneumoconiosis, and those with a smoking index of ≥200, as outlined in Table 2.

Further analysis revealed a higher proportion of urban and female patients aged 60 years and older. In urban areas, retired workers from state-owned enterprises were significantly more numerous than in rural regions (80.9% vs. 21.4%, χ²=3581.828, P<0.001). Similarly, the proportion of work-injury-insured workers was distinctly higher in urban areas versus rural (86.2% vs. 29.8%, χ²=3197.974, P<0.001). The proportion of retired female employees from state-owned enterprises surpassed that of males (62.2% vs. 47.0%, χ²=49.267, P<0.001), and more female patients were covered by work-related injury insurance than male patients (69.5% vs. 54.0%, χ²=24.688, P<0.001). This can potentially be attributed to the higher incidence of multimorbidity amongst urban patients and females.

In this study, 72.5% of patients working in state-owned enterprises benefitted from work-related injury insurance while only 35.2% and 26.8% did so in collective and private enterprises, respectively (χ²=366.263, P<0.001).

Figure 1 illustrates the patterns of multimorbidity, represented by various pairwise combinations of diseases or conditions, in both rural and urban settings. The most prominent combinations include four specific diseases: non-TB pulmonary infection, pulmonary heart disease, pulmonary bullae, pneumothorax, and hypertension. These were frequently observed in patients with pneumoconiosis from both urban and rural regions, albeit at higher proportions in urban patients. Moreover, the comorbidity of underweight and arthritis paired with non-TB lung infection and pulmonary heart disease were notably higher in rural patients. On the other hand, pairings of diabetes, cerebrovascular disease, obesity with hypertension, CVDs, COPD, and pulmonary infection were more commonly seen in urban patients, establishing several unique aggregate distributions.

Figure 1. 

Heatmap of the percentage of comorbid disease pairs and conditions by residence among pneumoconiosis patients in China.

Note: The proportions depicted by the green diagonal situated above and to the right of the gray diagonal represent patients residing in rural areas. Conversely, the proportions indicated by the brown diagonal below and to the left of the gray diagonal represent patients hailing from urban areas.

Abbreviation: COPD=chronic obstructive pulmonary disease; CVDs=cardiovascular diseases; PTB=pulmonary tuberculosis.