Yajia Lan

Cause-specific mortality in a Chinese chrysotile textile worker cohort

Chrysotile asbestos has continued to be mined and used in China, but its health effects on exposed workers have not been well documented. This study was conducted to give a complete picture about cause‐specific mortality in Chinese asbestos workers. A cohort of 586 males and 279 females from a chrysotile textile factory were prospectively followed for 37 years. Their vital status was identified, and the date and underlying cause of death were verified from death registry. Cause‐specific standardized mortality ratios by gender were computed with nationwide gender‐ and cause‐specific mortality rates as reference. Male workers were 11 years older, and had 6 years longer exposure duration than females; 79% in males and 1% in females smoked. In males, the mortality rate of all cancers doubled; both larynx and lung cancer were four‐fold, and mesothelioma was 33‐fold. In females, there was slightly excess mortality from lung cancer and all cancers, and significant increase in mesothelioma and ovarian cancer. Other significantly increased mortality was seen from cancers of thymus, small intestine and penis in males, and cancers of bone and bladder in females. In addition to asbestosis, mortality from pulmonary heart disease was significantly elevated in both genders. The data confirmed significantly excess mortality from mesothelioma in either gender, lung and larynx cancers in males, and ovarian cancer in females. A gender difference in mortality from lung cancer and all cancers could be mainly due to the discrepancies in age, exposure duration and smoking between the male and female workers.

Exposure–response relationship between chrysotile exposure and mortality from lung cancer and asbestosis

Objectives To describe mortality in workers exposed to chrysotile asbestos, and determine exposure–response relationships between asbestos exposure and mortality from lung cancer and asbestosis by fitting and comparing different models. Methods A prospective cohort consisting of 586 workers in an asbestos textile factory was followed from 1 January 1972 to 31 December 2006. A structured questionnaire was administered to collect personal information and exposure data. Paired concentration samples measured in the workshops were used to convert dust concentrations to fibre concentrations. Individual cumulative asbestos exposure was estimated as the product of fibre concentrations and duration of employment in each job and expressed as fibre-years/ml. The vital status of cohort members was followed annually. Poisson regression analysis was applied to fit log-linear, log-quadratic, power, additive relative risk and categorical models to estimate exposure–response relationships between cumulative fibre exposure and mortality from lung cancer and asbestosis. Results Of the 226 deaths (14.6 per 1000 person-years) over the 35-year follow-up, 51 were from lung cancer (3.29 per 1000 person-years) and 37 from asbestosis (2.39 per 1000 person-years). A significant exposure–response relationships with either lung cancer or asbestosis (p<0.001) was observed in the final model. The power model with lagged 10 years was found to be the best model of those evaluated for both lung cancer (β coefficient=0.53) and asbestosis (β coefficient=0.63). Conclusions The study confirmed strong associations between exposure to chrysotile asbestos and lung cancer and asbestosis, in which clear exposure–response relationships were observed.

Cancer Mortality in Chinese Chrysotile Asbestos Miners: Exposure-Response Relationships

Objective This study was conducted to assess the relationship of mortality from lung cancer and other selected causes to asbestos exposure levels. Methods A cohort of 1539 male workers from a chrysotile mine in China was followed for 26 years. Data on vital status, occupation and smoking were collected from the mine records and individual contacts. Causes and dates of death were further verified from the local death registry. Individual cumulative fibre exposures (f-yr/ml) were estimated based on converted dust measurements and working years at specific workshops. Standardized mortality ratios (SMRs) for lung cancer, gastrointestinal (GI) cancer, all cancers and nonmalignant respiratory diseases (NMRD) stratified by employment years, estimated cumulative fibre exposures, and smoking, were calculated. Poisson models were fitted to determine exposure-response relationships between estimated fibre exposures and cause-specific mortality, adjusting for age and smoking. Results SMRs for lung cancer increased with employment years at entry to the study, by 3.5-fold in ≥10 years and 5.3-fold in ≥20 years compared with <10 years. A similar trend was seen for NMRD. Smokers had greater mortality from all causes than nonsmokers, but the latter also had slightly increased SMR for lung cancer. No excess lung cancer mortality was observed in cumulative exposures of <20 f-yrs/ml. However, significantly increased mortality was observed in smokers at the levels of ≥20 f-yrs/ml and above, and in nonsmokers at ≥100 f-yrs/ml and above. A similarly clear gradient was also displayed for NMRD. The exposure-response relationships with lung cancer and NMRD persisted in multivariate analysis. Moreover, a clear gradient was shown in GI cancer mortality when age and smoking were adjusted for. Conclusion There were clear exposure-response relationships in this cohort, which imply a causal link between chrysotile asbestos exposure and lung cancer and nonmalignant respiratory diseases, and possibly to gastrointestinal cancer, at least for smokers.

Cancer mortality among Chinese chrysotile asbestos textile workers.

To determine mortality associated with exposure to chrysotile asbestos, a cohort of asbestos workers from an asbestos textile factory in China was followed prospectively from 1972 to 2008. A total 577 workers were successfully followed, achieving a follow-up rate of 98.5% over 37 years. Employment data and smoking information were obtained from factory and individual workers. Vital status was ascertained from factory personnel records and the municipal death registry. Workers were categorized into high, medium and low exposure groups in terms of their job titles and workshops. Follow-up generated 17,508 person-years, with 259 deaths from all causes, 96 all cancers and 53 lung cancers and 2 mesotheliomas. The highest cancer mortality was observed in the high exposure group, with 1.5-fold age-adjusted mortality from all cancers and 2-fold from lung cancer compared to the low exposure group. Age and smoking adjusted hazard ratio in the high exposure group was 2.99 (95%CI, 1.30, 6.91) for lung cancer and 2.04 (1.12, 3.71) for all cancers. Both smokers and nonsmokers at the high exposure level had a high death risk of lung cancer, with a clearer exposure-response trend seen in smokers. This study confirmed increased mortality from lung cancer and all cancers in asbestos workers, and the cancer mortality was associated with exposure level.

Adjusting outbreak detection algorithms for surveillance during epidemic and non-epidemic periods

Many aberration detection algorithms are used in infectious disease surveillance systems to assist in the early detection of potential outbreaks. In this study, we explored a novel approach to adjusting aberration detection algorithms to account for the impact of seasonality inherent in some surveillance data. By using surveillance data for hand-foot-and-mouth disease in Shandong province, China, we evaluated the use of seasonally-adjusted alerting thresholds with three aberration detection methods (C1, C2, and C3). We found that the optimal thresholds of C1, C2, and C3 varied between the epidemic and non-epidemic seasons of hand-foot-and-mouth disease, and the application of seasonally adjusted thresholds improved the performance of outbreak detection by maintaining the same sensitivity and timeliness while decreasing by nearly half the false alert rate during the non-epidemic season. Our preliminary findings suggest a general approach to improving aberration detection for outbreaks of infectious disease with seasonally variable incidence.

Hand, foot and mouth disease in China: evaluating an automated system for the detection of outbreaks

Abstract Objective To evaluate the performance of China’s infectious disease automated alert and response system in the detection of outbreaks of hand, foot and mouth (HFM) disease. Methods We estimated size, duration and delay in reporting HFM disease outbreaks from cases notified between 1 May 2008 and 30 April 2010 and between 1 May 2010 and 30 April 2012, before and after automatic alert and response included HFM disease. Sensitivity, specificity and timeliness of detection of aberrations in the incidence of HFM disease outbreaks were estimated by comparing automated detections to observations of public health staff. Findings The alert and response system recorded 106 005 aberrations in the incidence of HFM disease between 1 May 2010 and 30 April 2012 – a mean of 5.6 aberrations per 100 days in each county that reported HFM disease. The response system had a sensitivity of 92.7% and a specificity of 95.0%. The mean delay between the reporting of the first case of an outbreak and detection of that outbreak by the response system was 2.1 days. Between the first and second study periods, the mean size of an HFM disease outbreak decreased from 19.4 to 15.8 cases and the mean interval between the onset and initial reporting of such an outbreak to the public health emergency reporting system decreased from 10.0 to 9.1 days. Conclusion The automated alert and response system shows good sensitivity in the detection of HFM disease outbreaks and appears to be relatively rapid. Continued use of this system should allow more effective prevention and limitation of such outbreaks in China.

Improving the performance of outbreak detection algorithms by classifying the levels of disease incidence

We evaluated a novel strategy to improve the performance of outbreak detection algorithms, namely setting the alerting threshold separately in each region according to the disease incidence in that region. By using data on hand, foot and mouth disease in Shandong province, China, we evaluated the impact of disease incidence on the performance of outbreak detection algorithms (EARS-C1, C2 and C3). Compared to applying the same algorithm and threshold to the whole region, setting the optimal threshold in each region according to the level of disease incidence (i.e., high, middle, and low) enhanced sensitivity (C1: from 94.4% to 99.1%, C2: from 93.5% to 95.4%, C3: from 91.7% to 95.4%) and reduced the number of alert signals (the percentage of reduction is C1∶4.3%, C2∶11.9%, C3∶10.3%). Our findings illustrate a general method for improving the accuracy of detection algorithms that is potentially applicable broadly to other diseases and regions.

Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort

Objectives To examine mortality from digestive cancers in a Chinese miner cohort and to explore the exposure–response relationship between chrysotile mining dust and site-specific digestive cancers. Methods A cohort of 1539 asbestos miners was followed for 26 years. Information on vital status and death causes was collected from personnel records and hospitals. Underlying causes of death from cancers were determined by combination of clinical manifestations and pathological confirmation. Individual cumulative dust exposures were estimated based on periodic dust measurements of different workshops, individuals’ job title and employment duration, and treated as a time-dependent variable. Standardised mortality ratios (SMR) were calculated according to Chinese national data and stratified by exposure (levels 1–3, from low to high). Cox proportional hazard models were constructed to estimate HRs in relation to cumulative exposure with adjustment of smoking. Results Fifty-one deaths from digestive cancers were identified in the cohort, giving an SMR of 1.45 (95% CI 1.10 to 1.90). There was a clear exposure–response relationship between asbestos dust exposure and mortality from stomach cancer, with SMR of 2.39 (95% CI 1.02 to 5.60) and 6.49 (2.77 to 15.20) at exposure levels 2 and 3, respectively. The clear relationship remained in multivariate analysis, in which workers at the highest exposure level had HRs of 12.23 (95% CI 8.74 to 17.12). In addition, excess mortality from oesophageal and liver cancers was also observed at high exposure levels. Conclusions This study provides additional evidence for the association between exposure to chrysotile mining dust and excess mortality from digestive cancers, particularly stomach cancer.

Cancer Mortality and Asbestosis Among Workers in an Asbestos Plant in Chongqing, China

OBJECTIVE To investigate whether asbestosis is a risk factor for mortality of lung cancer. METHODS A fixed cohort study was established in an asbestos plant in Chongqing, China, and followed up for 30 years from the beginning of 1972. Basic personal information on life state, cause of death, and diagnosis of asbestosis was collected. Multiple logistic regressions were applied to analyze risk factors. RESULTS During the 30-year follow-up, 584 male workers constituting a total of 14,664 person-years were monitored and data were analyzed. Among them, 203 (34.8%) died and the mortality rate was 13.8 per 1000 person-years, cancer accounting for 37.4%. Excess risks were observed for lung cancer (OR = 3.72) and nonmalignant respiratory diseases (OR = 2.73) among workers with asbestosis. High-exposure level was another risk factor for lung cancer (OR = 3.20). Workers with category II of asbestosis demonstrated a higher OR of both lung cancer and nonmalignant respiratory diseases than those with category I of asbestosis. CONCLUSION High asbestos exposure level and asbestosis were the risk factors for death of lung cancer and nonmalignant respiratory diseases. Asbestosis is an independent risk factor for lung cancer among Chinese workers exposed to chrysotile, the risk increases with the increasing profusion of opacities of lung.

Analysis of mortality in chrysotile asbestos miners in China

In order to investigate the mortality of a cohort of chrysotile asbestos miners in China and evaluate its association with exposure to chrysotile, a fixed cohort of 1932 workers in chrysotile asbestos mine was established in 1981 and followed till June 1, 2010. Information on vital status, cause of death and smoking habits was collected. The workers were divided into two groups according to their exposure status. The exposed group was composed of frontline workers who worked directly on mining or processing asbestos products. The control group consisted of those who were not directly exposed to asbestos in their work. Standardized mortality ratio (SMR) was calculated according to Chinese national death rates. Cox proportional hazards model was applied to estimate the adjusted relative risks of deaths from major causes in exposed and control groups. The results of this study showed that main causes of mortality were malignant neoplasm, cardiovascular disease, cerebrovascular disease and respiratory disease for chrysotile miners. The mortality rate was 939.20 per 100 000 person-years for workers. The SMR for all causes of death was 1.46 in the cohort. Statistically significant mortality excesses were found for lung cancer (SMR=1.51), pulmonary heart disease (SMR=2.70), respiratory disease (SMR=1.93), asbestosis (SMR=9.62), and accident (SMR=1.59). The mortalities from malignant neoplasm, lung cancer, cerebrovascular disease and digestive disease in the exposed group were significantly higher than those in the control group. The findings indicate that chrysotile exposure is a risk factor for lung cancer, respiratory disease, cerebrovascular disease and digestive disease.SummaryIn order to investigate the mortality of a cohort of chrysotile asbestos miners in China and evaluate its association with exposure to chrysotile, a fixed cohort of 1932 workers in chrysotile asbestos mine was established in 1981 and followed till June 1, 2010. Information on vital status, cause of death and smoking habits was collected. The workers were divided into two groups according to their exposure status. The exposed group was composed of frontline workers who worked directly on mining or processing asbestos products. The control group consisted of those who were not directly exposed to asbestos in their work. Standardized mortality ratio (SMR) was calculated according to Chinese national death rates. Cox proportional hazards model was applied to estimate the adjusted relative risks of deaths from major causes in exposed and control groups. The results of this study showed that main causes of mortality were malignant neoplasm, cardiovascular disease, cerebrovascular disease and respiratory disease for chrysotile miners. The mortality rate was 939.20 per 100 000 person-years for workers. The SMR for all causes of death was 1.46 in the cohort. Statistically significant mortality excesses were found for lung cancer (SMR=1.51), pulmonary heart disease (SMR=2.70), respiratory disease (SMR=1.93), asbestosis (SMR=9.62), and accident (SMR=1.59). The mortalities from malignant neoplasm, lung cancer, cerebrovascular disease and digestive disease in the exposed group were significantly higher than those in the control group. The findings indicate that chrysotile exposure is a risk factor for lung cancer, respiratory disease, cerebrovascular disease and digestive disease.