Project progress, August 2014

Workplace exposure to airborne dust, asbestos, diesel engine exhaust and many other chemicals is associated with greater risk of disease. Construction workers are often more likely than others to come into contact with these hazards and may suffer a greater burden of disease as a consequence.
However, in most cases it is impossible to reliably attribute individual cases of disease to a particular cause. If we are to properly understand how many people suffer ill health from these exposures we must use indirect statistical methods to estimate the impacts.


Our study aims to estimate the current and future number of cases of occupational cancer and selected non-malignant respiratory diseases (NMRD) for Singapore from workplace exposure in the construction and shipbuilding/repair industries. The primary measure of the burden of disease used in this project will be the attributable fraction, i.e. the proportion of disease cases that would not have occurred had the workers not been exposed. The attributable fraction will be used to estimate attributable numbers of cases of disease and deaths using information about the numbers of workers employed in these sectors and other data we have collected. 

In January of this year a series of focus group discussions were held with local experts on the Singaporean construction industry. Information from these discussions along with published literature was compiled to provide an overview of the history of construction in Singapore over the last 50 years and projected changes over the next 20 years. 

This document was intended to inform later stages of our research and has already been a useful resource for ensuring inclusion of the Singaporean context during the stages of research described below.

Some important steps in the methodology are to a) determine the proportion of the working population exposed over the last 40 years, which we call the risk exposure period (REP), b) obtain risk estimates of disease due to exposures of interest from the epidemiological literature, and c) determine the exposure prevalence (i.e. the proportion exposed among those employed in that occupation) and intensity (i.e. the annual mean level of exposure) among the exposed.

Knowledge of the numbers of workers who were exposed to particular hazardous agents and from this, determination of the proportion of the working population exposed, is an important requirement for the estimation of the burden of disease. In April 2014 we prepared a report for the Workplace Safety and Health Institute (WSHI), our funding agency, summarising employment statistics in Singapore for the industries relevant to our study over the REP. Our sources for this information included data from the National Census, Labour Force Survey, and General Household Survey. At the end of July 2014 we presented two more progress reports: the first described the disease risk estimates we selected from the epidemiological literature accompanied by an explanation for their selection, and the second was a report outlining our plans to develop a job exposure matrix (JEM) for the industries relevant to our study in Singapore to enable us to estimate the prevalence and intensity of exposure.

Our approach for selecting disease risk estimates was guided by our previous involvement with the UK Cancer Burden study (Rushton et al., 2012 ) and the Global Burden of Disease assessment (Lim et al., 2013 ). After reviewing the epidemiological literature over the past several months, we summarized the data that we plan to rely upon. The selection of studies depended on several factors including: the intensity and duration of exposure in the study population, whether the final risk estimates were robust, and their appropriateness for workers in the relevant industries in Singapore. 

The risk estimates were identified in terms of pairs of exposures and diseases, e.g. asbestos and lung cancer or working as a painter and bladder cancer. For occupational cancers relevant to our study, we identified 29 pairs and for NMRD there were 21 pairs, plus silicosis amongst granite quarry workers and asbestosis amongst asbestos cement factory workers. The risk estimates will continue to be refined and reviewed as we finalise the methodology for the JEM and burden estimation.

Our plan to develop a JEM along with a summary of progress was outlined in the second progress report submitted to WSHI in July. A JEM is a tool used to transform occupational titles into estimates of exposure to substances harmful to human health, and can be used in epidemiological studies. We are developing a JEM for the construction and shipbuilding/repair industries in Singapore, in which occupational titles from the Singapore Standard Occupational Classification can be used to obtain estimates of the prevalence for exposures of interest as well as a semi-quantitative estimate of the intensity of exposure. The JEM will cover substances that are relevant for both cancer and NMRDs. In addition, we will estimate the overall average (geometric mean) exposure, the variability in exposures (geometric standard deviation) and the rate of temporal change in average exposure for the exposures in the key sectors. The final JEM will be developed by the end of October 2014, at the halfway point of our two-year project. 

The Principal Investigator for this work was Professor John Cherrie of the IOM. The main work of the project was completed in 2016 and a report submitted to the Workplace Safety and Health Institute (WSHI). Further information on the results of the study are contained in the presentation made at the Workplace Safety and Health conference, held in Singapore, August 2016, summarised in this presentation.

The results from the study will be published in the scientific literature in due course. Further information about the project can also be obtained from Professor John Cherrie, email john.cherrie@iom-world.org.