Case-crossover study for the association between increased hospital admissions for respiratory diseases and the increase in atmospheric PM 2.5 and PM 2.5 -bound trace elements in Pretoria, South Africa.

Outdoor PM _2.5 was sampled in Pretoria, 18 April 2017 to 28 February 2020. A case-crossover epidemiology study was associated for increased PM _2.5 and trace elements with increased hospital admissions for respiratory disorders (J00-J99). The results included a significant increase in hospital admissions, with total PM _2.5 of 2.7% (95% CI: 0.6, 4.9) per 10 µg·m ^-3 increase. For the trace elements, Ca of 4.0% (95% CI: 1.4%-6.8%), Cl of 0.7% (95% CI: 0.0%-1.4%), Fe of 3.3% (95% CI: 0.5%-6.1%), K of 1.8% (95% CI: 0.2-3.5) and Si of 1.3% (95% CI: 0.1%-2.5%). When controlling for PM _2.5 , only Ca of 3.2% (95% CI: 0.3, 6.1) and within the 0-14 age group by 5.2% (95% CI: 1.5, 9.1). Controlling for a co-pollutant that is highly correlated with PM2.5 does reduce overestimation, but further studies should include deposition rates and parallel sampling analysis.