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.