Mortality from non-malignant respiratory diseases among people with silicosis in Hong Kong: exposure-response analyses for exposure to silica dust

Association of spirometric restriction with mortality in the silicotics: a cohort study

BACKGROUND

Restrictive spirometry pattern (RSP), defined as reduced forced vital capacity (FVC) in absence of airflow obstruction (AFO), is associated with increased risk of mortality in general population. However, evidence in the patients with silicosis is limited. This study was aimed to investigate the relationship between RSP and the risk of death in a silicotic cohort.

METHOD

This retrospective cohort study used data from the Pneumoconiosis Clinic, Hong Kong Department of Health that containing 4315 patients aged 18-80 years and diagnosed with silicosis during 1981-2019, with a follow-up till 31 December 2019. Spirometry was carried out at the diagnostic examination of silicosis. Lung function categories were classified as normal spirometry (FEV1/FVC ≥ 0.7, FVC ≥ 80% predicted), RSP only (FEV1/FVC ≥ 0.7, FVC < 80% predicted), AFO only (FEV1/FVC < 0.7, FVC ≥ 80% predicted), and RSP&AFO mixed (FEV1/FVC < 0.7, FVC < 80% predicted). The hazard ratio (HR) and 95% confidence intervals (95% CI) were computed using a Cox proportional hazards model adjusting for age, body mass index, history of tuberculosis, smoking status, pack-years, and radiographic characteristics of silicotic nodules.

RESULTS

Among the 4315 patients enrolled in the study, the prevalence of RSP was 24.1% (n = 1038), including 11.0% (n = 473) with RSP only and 13.1% (n = 565) with mixed RSP and AFO. During the follow-up period, a total of 2399 (55.6%) deaths were observed. Compared with the silicotics with normal spirometry, those with RSP only had significantly increased risk of all-cause mortality (HR = 1.63, 95% CI 1.44-1.85) and respiratory-related mortality (HR = 1.56, 95% CI 1.31-1.85). Notably, a higher risk of mortality was observed in silicotics with mixed ventilatory defects of both RSP and AFO (all-cause mortality: HR = 2.22, 95% CI 1.95-2.52; respiratory-related mortality: HR = 2.59, 95% CI 2.18-3.07) than in those with RSP only.

CONCLUSION

RSP is significantly associated with increased risk of all-cause and respiratory-related mortality in the silicotics, and patients with mixed restrictive and obstructive ventilatory defect have higher risk of mortality than those with single RSP or AFO. These findings emphasize the importance of recognizing RSP in the occupational settings, especially for the silicotic patients with mixed ventilatory defect.

Adherence to Inhaled Therapy in Patients with COPD Associated to Pneumoconiosis

Background

Pneumoconiosis has high prevalence of chronic obstructive pulmonary disease (COPD), respiratory morbidity, and mortality.

Objective

The aim of the present study was to examine patient characteristics and adherence to inhaled therapy among pneumoconiosis with COPD in a real-world clinical setting.

Methods

A cohort of pneumoconiosis patients with COPD prescript with at least one type of long-acting inhaled drug was followed for adherence for 2 years. Demographic and COPD-related characteristics were collected in baseline.

Results

In baseline, after adjusting for age, dust exposure duration positively correlated with number of acute exacerbation (AE) frequency in the last year. There were close associations among COPD Assessment Tool (CAT) score, modified Medical Research Council Dyspnea Scale (mMRC) grade, number of AE, and pre-FEV₁ value. Of 296 participants originally recruited, 213 participants finished the 2-year follow-up for adherence. 122 (57.28%) were non-adherent to inhaled therapy. The most common reason for non-adherence was “relief of symptoms after short-term controller medication use” (53.28%). Patients who were non-adherent reported higher body mass index (BMI), less AE events in the last year, higher pre-FEV₁ value, higher post-FEV₁ value and low CAT, mMRC scores compared to adherent in baseline. High pre-FEV₁ value (OR = 1.04, CI = 1.018–1.064) and low mMRC scores (OR = 0.406, CI = 0.214–0.771) were risk factors found associated with non-adherence.

Conclusion

A majority of pneumoconiosis patients complicated with COPD have suboptimal inhaled therapy adherence. Evidence-based, adherence-enhancing interventions should be targeted on less severe subjects.

Association of silica dust exposure with mortality among never smokers: A 44-year cohort study

The association of silica dust exposure with mortality among never smokers has not been well established. We aimed to evaluate the association of silica dust exposure with mortality among never smokers. We studied 17,130 workers employed for at least 1 year between January 1, 1960 and December 31, 1974, with follow-up until the end of 2013. Cumulative respirable silica dust exposure (CDE) was estimated by linking a job-exposure matrix to personal work history. We observed 3937 deaths during 589,357.26 person-years of follow-up. Significant positive exposure-response relationships were found between CDE and mortality from all cause (HR = 1.01, 95%CI = 1.01-1.02), respiratory tuberculosis (HR = 1.04, 95%CI = 1.02-1.06), CVDs (HR = 1.03, 95%CI = 1.02-1.04), and diseases of the respiratory system (HR = 1.06, 95%CI = 1.04-1.07). We found higher standardized mortality ratios for respiratory tuberculosis (2.62, 2.32-2.95), CVDs (1.43, 1.32-1.54), and pneumoconiosis (77.75, 68.21-88.25) among silica dust exposed workers. In addition, we estimated that 4.19%, 20.69%, 7.48% and 34.06% of deaths for all cause, respiratory tuberculosis, CVDs, and diseases of the respiratory system among Chinese workers were attributed to silica, after adjusting for other covariates. With regard to lung cancer, compared with unexposed group, the HRs and 95% CI were 0.94 (0.52-1.71), 1.86 (1.15-3.00), 1.65 (0.95-2.86) for low, medium, and high exposed workers, respectively. Long-term silica dust exposure is associated with increased mortality in the absence of cigarette smoking.

Mortality from silicosis in Brazil: Temporal trends in the period 1980-2017

BACKGROUND

Silicosis is the most prevalent pneumoconiosis in Brazil. We aimed to estimate mortality rates and temporal trends for silicosis, and to identify areas of highest mortality.

METHODS

Records of silicosis as the underlying (1980-2017) or contributory (2000-2017) cause of death in adults aged 20 years and older were retrieved from the Brazilian Mortality Database. Age-standardized mortality rates (ASMR) were calculated. The annual trend in ASMR was analyzed by joinpoint regression. Mortality rates per 100,000 person-years were calculated for each municipality. We analyzed temporal trends in municipalities where similar activities with exposure to silica were performed.

RESULTS

There were 3164 death records (96.6% men) distributed over 14% of the municipalities. Mean age of death was 59.2 (SD 15.1) and mean ASMR was 0.085/100,000 (confidence interval 0.080-0.091). Joinpoint regression showed a significant increase in ASMR from 1980 to 2006 and a significant decrease after 2006 driven by a decline in deaths of individuals younger than 70 years. The highest mortality rate was 21.83/100,000 person-years, in a municipality with small mining operations for gems. Gold mining municipalities showed the highest composite death rate, 4.0/100,000 person-years. Tuberculosis was the main cause of death when silicosis was a contributing cause.

CONCLUSIONS

In contrast with developed countries, silicosis mortality in Brazil increased to 2006 and subsequently started to drop, mostly from a plateau or decrease in deaths occurring in municipalities which regulated economic activities. However, this decrease did not occur in the older age group nor in the unregulated sector, the latter being the main challenge for exposure control and surveillance.

Smoking cessation sharply reduced lung cancer mortality in a historical cohort of 3185 Chinese silicotic workers from 1981 to 2014

BACKGROUND

Population-based studies showed an over 50% decrease in lung cancer risk after quitting smoking for 5-6 years, but the beneficial effect in silicotics remains unknown. We aimed to rectify this knowledge gap using a large historical cohort of 3185 Chinese silicotics since 1981 and followed-up till 2014.

METHODS

Baseline information on workers' socio-demographics, smoking habits, occupational history, and medical history was collected. Smoking status was reassessed during follow-up. Multiple Cox proportional hazards model was performed to evaluate the impact of smoking cessation on lung cancer mortality.

RESULTS

Overall, 1942 deaths occurred and 188 lung cancer deaths were identified. Compared with never quitters, silicotics who were new quitters had almost halved their lung cancer risk [hazard ratio (HR) = 0.51, 95%CI: 0.34-0.76], while persistent quitters had a 53% risk reduction (HR = 0.47, 95%CI: 0.33-0.66). Lung cancer mortality approximately halved after quitting smoking for 10 years. While the risk kept decreasing with years since cessation, it did not reverse back to that of never smokers. Persistent quitters with small opacities tended to have higher beneficial effects than those with large opacities.

CONCLUSIONS

Smoking cessation for 10 years halved lung cancer mortality among silicotics, while the beneficial effect was prominent for patients with small opacities.

A case-control study of airways obstruction among construction workers

BACKGROUND

While smoking is the major cause of chronic obstructive pulmonary disease (COPD), occupational exposures to vapors, gases, dusts, and fumes (VGDF) increase COPD risk. This case-control study estimated the risk of COPD attributable to occupational exposures among construction workers.

METHODS

The study population included 834 cases and 1243 controls participating in a national medical screening program for older construction workers between 1997 and 2013. Qualitative exposure indices were developed based on lifetime work and exposure histories.

RESULTS

Approximately 18% (95% CI = 2-24%) of COPD risk can be attributed to construction-related exposures, which are additive to the risk contributed by smoking. A measure of all VGDF exposures combined was a strong predictor of COPD risk.

CONCLUSIONS

Construction workers are at increased risk of COPD as a result of broad and complex effects of many exposures acting independently or interactively. Control methods should be implemented to prevent worker exposures, and smoking cessation should be promoted.

Joint effects of smoking and silicosis on diseases to the lungs

Smokers are subject to being more susceptible to the long-term effects of silica dust, whilst it remains unclear whether the joint effect of smoking and silicosis differs amongst diseases to the lungs; this study aims to address this knowledge gap. This was a historical cohort study comprised of 3202 silicotics in Hong Kong during 1981-2005 who were followed up till 31/12/2006. We estimated the standardized mortality ratio (SMR) in the smoking and never smoking silicotics using the mortality rates of male general population indiscriminately by smoking status, but these SMRs were regarded as biased. We adjusted these biased SMRs using "smoking adjustment factors (SAF)". We assessed the multiplicative interaction between smoking and silicosis using 'relative silicosis effect (RSE)' that was the ratio of SAF-corrected SMR of smoking silicotics to the never smokers. A RSE differs significantly from one implies the presence of multiplicative interaction. A significant excess SMR was observed for respiratory diseases (lung cancer, chronic obstructive pulmonary diseases [COPD], silicosis) and other diseases to the lungs (pulmonary heart disease, tuberculosis). All the 'biased-SMRs' in smokers were higher than those in never smokers, but the SAF-corrected SMRs became higher in never smokers. The RSE was 0.95 (95%CI: 0.37-3.55), 0.94 (95%CI: 0.42-2.60), and 0.81 (95%CI: 0.60-1.19) for lung cancer, COPD, and silicosis; whilst it was 1.21 (95%CI: 0.32-10.26) for tuberculosis and 1.02 (95%CI: 0.16-42.90) for pulmonary heart disease. This study firstly demonstrated the joint effect of smoking and silicosis may differ amongst diseases to the lungs, but power is limited.

Pathological mechanisms of liver injury caused by continuous intraperitoneal injection of silica nanoparticles

Crystalline silica is well known to induce chronic lung inflammation by inhalation that can progress to silicosis. Recently, we reported that silica nanoparticles (SN) cause more damage to liver instead of lung when they enter the body by intravenous injection. However, this mechanism is still unclear. In the present study, liver damages caused by mesoporous hollow silica nanoparticles (MHSNs) were demonstrated after continuous intraperitoneal injection into mice twice a week for 6 weeks. The administration of MHSNs at 50 mg/kg increased liver injury markers in serum, such as alanine aminotransferase (ALT), inflammatory cytokines interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α). Histological analysis revealed lymphocytic infiltration and silicotic nodular like lesions in liver. Collagen fibers were observed around the silicotic nodular like lesion, and hydroxyproline level in liver was also increased dramatically. We also found that activated kupffer cells (KCs) played a key role in the liver damage caused by SNs similar to alveolar macrophage in the process of silicosis. These suggest that the mechanism of liver damage caused by SNs is in consonance with the occurrence of silicosis. These findings may provide useful information for the further toxicity and bioapplication research of nanoparticles.

Lung cancer mortality among silicotic workers in Hong Kong--no evidence for a link

BACKGROUND

The link between silica dust/silicosis and lung cancer is still very controversial. We examined the relationship between silica dust exposure and/or silicosis and lung cancer in a large cohort of silicotic workers in Hong Kong.

PATIENTS AND METHODS

All workers with silicosis in Hong Kong diagnosed during the period 1981-1998 were followed up till the end of 1999 to ascertain their vital status and causes of death. Standardized mortality ratio (SMR) for lung cancer and other major causes of death were calculated. Axelson's indirect method was used to adjust for smoking effect. Multiple Cox regression models were carried out to examine the exposure-response relationship between silica dust and lung cancer.

RESULTS

About 10% (86) of all 853 deaths were from lung cancer, giving a SMR of 1.69 [95% confidence interval (CI) 1.35-2.09]. Lung cancer SMR for caisson and surface construction workers were 2.39 (95% CI 1.50-3.62) and 1.61 (95% CI 1.21-2.10), respectively, which became 1.56 (95% CI 0.98-2.36) and 1.09 (95% CI 0.82-1.42) after adjusting for smoking. No consistent exposure-response relationship was detected between silica dust or severity of silicosis and lung cancer death.

CONCLUSION

Our cohort study did not offer positive support to a link between silica or silicosis and lung cancer.