| Summary: | Student Number : 0316118X -
MPH research report -
School of Public Health -
Faculty of Health Sciences === Introduction: On the weekend of 16 – 17 December 1995, the community of Macassar
was exposed to elevated levels of sulphur dioxide vapours (SO2) caused by a fire on a
nearby stockpile for approximately 21.5 hours. It has been estimated that community
members were exposed to levels as high as 200 parts per million (ppm) of this gas as
some 15 000 tons of the sulphur stockpile ignited. This resulted in a toxic plume of SO2
being blown over the Macassar area by the prevailing wind. The aim of this study was to
assess the environmental and host factors associated with persistent lower respiratory
symptoms among residents of this community six years after being acutely exposed to
elevated exposures of SO2 vapours.
Materials and methods: A case-control study was conducted. The cases and controls
were selected from adult residents who reported to the Macassar disaster project clinic for
a health assessment in order to lodge a medico-legal claim. Survey instruments included a
questionnaire, clinical examination and clinical record review by an expert panel. A case
was defined as an adult resident who presented to the clinic for an examination with
persistent (at year 1 and 6 after the disaster) lower respiratory symptoms. Controls were
chosen from clinic attendees without lower respiratory symptoms at year 1 and 6.
Environmental exposure was calculated by using the Industrial Source Complex Short
Term Model (ISCST 3) to predict time-averaged concentrations at specified receptor
locations. Multiple logistic regression was used to investigate the association between
lower persistent respiratory symptoms, host and environmental factors (estimated
concentration and duration of exposure to SO2). Results: A total of 76 cases and 180 controls were selected. The cases and controls were
comparable with respect to age, gender, height and smoking status. The results indicated
that a medical history of pulmonary tuberculosis at least one year prior to the fire (OR:
3.5, CI: 1.5-8.4) was significantly associated with having persistent lower respiratory
symptoms. Furthermore, subjects with persistent lower respiratory symptoms were nine
times more likely to report symptoms of tight chest (OR: 9.9; CI: 5.2-19.1), and twice as
likely to report shortness of breath (OR: 2.0; CI: 1.0-4.1) at the time of the fire. None of
the exposure metrics (total hours of exposure, cumulative exposure, peak exposure) were
significantly associated with persistent lower respiratory symptoms. However, peak SO2
exposure estimated at hour 15 was significantly associated with persistent lower
respiratory symptoms (OR: 1.0; CI: 1.0-1.1).
Discussion: The results of this study are consistent with previous studies reporting lower
respiratory tract symptoms after chemical exposure irrespective of age or smoking status.
Furthermore, as in other studies respiratory health status was a significant factor in
determining susceptibility to SO2 exposure. Various reports in the literature suggest that
exposure > 20 ppm is associated with chronic respiratory symptoms. This however was
not demonstrated in this study, using estimates of exposure calculated using the ISCST
model suggesting possible exposure misclassification. “Self-selection” bias was an
important limitation in this study, since the entire study population was self-referred and
as such the study population was not randomly selected. Another limitation is the
possibility that there may be potential recall bias operating since the fire incident
happened six years ago; however this was considered unlikely as there was nondifferential
reporting between cases and control. Self reported symptoms on the
questionnaires might have been over-reported due to fear, anxiety and stress or secondary gain related to compensation issues. The lack of association between exposure variables
and persistent asthma may have also been due to lack of power (small sample size),
although this was thought to be a minor contributory factor.
Conclusion: Host-related factors such as a previous history of pulmonary TB and acute
asthma-like symptoms at the time of the fire were important predictors of persistent lower
respiratory symptoms reported by residents 6 years after acute exposure to SO2 vapours
emanating from a sulphur fire.
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