Does apparent temperature modify the effects of air pollution on respiratory disease hospital admissions in an industrial area of South Africa?

Abstract

Background: Temperature and air pollution are often treated as separate risk factors and very few studies have investigated effect modification by temperature on air pollution, and the impact of this interaction on human health in Africa. This study therefore investigated the modifying effects of temperature on the association between air pollution and Respiratory disease (RD) hospital admission in South Africa.

 Methods: RD admission data (ICD10 J00-J99) were obtained from two hospitals located in Secunda, South Africa beween 1 January 2011 to 31 October 2016. NO₂, SO₂, PM₁₀, PM_2.5, temperature and relative humidity data were obtained from the South African Weather Services. A case-crossover epidemiological study design was applied and lag0-1 was used. Models were adjusted for public holidays and  Apparent Temperature (Tapp). Tapp was classified as warm (Tapp>75^th percentile), cold (Tapp<25^th percentile) and normal (Tapp  25^th-75^th  percentile).

Results: Of the 14 568 RD admissions, approximately equal number of females and males were admitted. The average daily NO₂, SO₂, PM_2.5 and PM₁₀ levels were 12.4 μm/m³, 8.5 μm/m³, 32.3 μm/m³ and 68.6 μm/m³, respectively. Overall, a 10 μm/m³ increase in SO₂ on warm days was associated with an increase in RD hospital admissions among the patients by 8.5% (95% Conf. Int: 0.4%, 17.2%) and 8.4% (95% Conf. Int: 0.3%, 17.1%) after adjustment for PM_2.5 and PM₁₀ respectively. However, increasing PM_2.5 or PM₁₀ by 10 μm/m³ was associated with an increase in RD hospital admissions when the temperature was normal after adjusting for SO₂.  On cold days there were significant associations between the SO₂ and RD admissions among the 0-14 year age group after adjusting for either PM_2.5 (6.5%; 95% Conf.Int: 0.9%, 12.4%) or PM₁₀ (5.5%; 95% Conf.Int: 0.3%, 11.1%).

Conclusions: SO₂ was affected by extremes of temperature while the particulate matters had effect on RD admission during normal temperature in Secunda.