Introduction: Residents of Macassar, South Africa, were exposed to sulphur dioxide vapours (SO₂) caused by an ignited sulphur stockpile, which produced peak hourly SO₂ levels of 20⁻200 ppm. The aim of this study was to assess the risk factors associated with persistent lower respiratory symptoms (LRS) or asthma six years after acute exposure to high SO₂ levels. Methods: A case-control study of residents that presented for a health evaluation six years after the incident was conducted. Survey instruments included a questionnaire, clinical examination and medical record review by an expert panel. A "case" was defined as a resident with persistent LRS/asthma. The Industrial Source Complex Short Term Model (ISCST 3) was used to predict time-averaged hourly SO₂ levels. Results: A previous history of pulmonary tuberculosis (PTB) was associated with persistent LRS/asthma (ORudj: 3.49, CI: 1.46⁻8.35). Cases were more likely to report chest tightness (ORudj: 9.93; CI: 5.15⁻19.11) at the time of the incident. Peak exposure at hour 15 was associated with persistent LRS/asthma (ORadj: 1.04; CI: 1.01⁻1.07). Conclusion: LRS/asthma persisted in some individuals six years after acute SO₂ exposure. Aside from peak exposures, initial chest tightness and a previous history of PTB were the strong predictors of persistent LRS/asthma.
Keywords: asthma; exposure; persistent lower respiratory symptoms; sulphur dioxide.