Temperature modifies the association between air pollution and cardiovascular disease hospital admissions in the Vaal Triangle Air Pollution Priority Area, South Africa

Abstract

Background: Very few studies in Africa investigated effect modification by a temperature indicator (e.g. apparent temperature, Tapp) on the human health effects of air pollution. Due to climate change, an increase of 3-4°C in ambient temperature is projected along the South African coast and 6-7°C inland during the next 80 years. Methods: Cardiovascular disease (CVD) hospital admission data (ICD10 I00-I99) were obtained from a private hospital group; after ethics approval. The study period was 1 January 2011 to 31 October 2016. NO2, SO2, PM2.5, PM10, temperature and relative humidity data were obtained from the Department of Environmental Affairs. A case-crossover epidemiological study design was applied. The present study focused on lag0-1; as most other studies. Models were adjusted for public holidays and Tapp. Days with Tapp below and above/equal the 25th (9.6°C) and 75th percentiles (20.1°C) were classified as cold and warm days, respectively. Results: Of the 15 237 admissions, 45.9% were from women and 39.0% from 15-65 year olds. The daily NO2, SO2, PM2.5 and PM10 levels were 30.3, 17.1, 35.4 and 60.8 μm/m3, respectively, and exceeded the WHO guidelines between 25% to 50% of the days. None of the air pollutants had significant associations with CVD admissions on cold or warm days. The elderly appeared to be more at risk to PM10 on normal days compared to all groups combined, e.g. RR 1.037 95%CI 1.009-1.065 per 10 μm/m3 increase compared to the unstratified analyses RR 1.017 95%CI 1.001-1.035. The same was observed for males RR 1.026 95%CI 1.003-1.050. PM2.5 had a stronger association than PM10 among the elderly on normal days: RR 1.068 95%CI 1.008-1.133. Conclusions: These results indicate that the risk of CVD admissions due to ambient air pollution exposure is different on cold, normal and warm days in Cape Town.