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Impact of air pollution may be worse than previously thought

Air pollution increases hospital admissions even at levels below guidelines and for a wider range of conditions

Ingrid Torjesen

Thursday, 28 November 2019

Short-term exposure to fine particulate matter in the air (known as PM2.5) has been found to be associated with several newly identified causes of hospital admissions, even at levels below international air quality guidelines, a US study* published by The BMJ has found.

As well as confirming several previously established causes of hospital admission associated with short-term exposure to PM2.5, including heart and lung diseases, diabetes, Parkinson's disease, and diabetes, the study also found that exposure was also associated with increased admissions for conditions not previously linked to air pollution, including sepsis, kidney failure, urinary tract and skin infections.

As a result, the researchers suggest that the World Health Organisation (WHO) air quality guidelines need revising.

The researchers from the Harvard Chan School of Public Health analysed more than 95 million Medicare hospital insurance claims for adults aged 65 or older in the United States from 2000 to 2012. Causes of hospital admission were classified into 214 mutually exclusive disease groups and these were linked with estimated daily exposure to PM2.5 based on data from the US Environmental Protection Agency.

The researchers then estimated the increased risk of admission and the corresponding costs associated with a 1 µg/m3 increase in short-term exposure to PM2.5 for each disease group.

They found that each 1 µg/m3 increase in PM2.5 was associated with 2,050 extra hospital admissions, 12,216 days in hospital, and $31m (£24m, €28m) in care costs for diseases not previously associated with PM2.5 including sepsis, kidney failure, urinary tract and skin infections.

What's more, these associations remained even when the analysis was restricted to days when the PM2.5 concentration was below the WHO air quality guideline, suggesting that they need updating, say the researchers.

Although they pointed out that the study had been unable to fully capture costs after discharge, or take account of other factors that could trigger hospital admission, such as smoking, alcohol consumption, and drug use, they say that the study had a large sample size, looked at data over a 13-year period and results remained similar after further analyses, suggesting that they are robust.

The study "discovered several new causes of hospital admissions associated with short-term exposure to PM2.5 and confirmed several already known associations, even at daily PM2.5 concentrations below the current WHO guideline," the researchers conclude.

They explain that these newly associated diseases represent around a third (31-38%) of the total PM2.5 associated effect, suggesting that current figures for PM2.5 associated illness "might be considerable underestimates."

Commenting on the findings Dr Suzanne Bartington, clinical research fellow and honorary consultant in public health, University of Birmingham, said: “This study adds to an emerging body of evidence concerning health risks of pollutant exposure below existing PM2.5 guideline levels. The relationships between risks posed by short and long-term (chronic exposure) and the sub-clinical or physiological outcomes are difficult to capture in existing epidemiological research approaches and require future investment in research to enable more accurate assessment. However, it is evident from the findings of this and many previous studies that reducing fine PM concentrations is essential to improving health and reducing healthcare costs among populations worldwide.”

“These results add to the growing body of scientific evidence showing adverse health effects of air pollutants below current air quality policy target values,” Dr Stefan Reis, science area head for atmospheric chemistry and effects, Centre for Ecology & Hydrology, said. “The findings suggest that interventions reducing pollution levels even in areas where they are already low will contribute to reduced public health impacts and costs.”

*Wei Y, Wang Y, Qian D, et al. Short term exposure to fine particulate matter and hospital admission risks and costs in the Medicare population: time stratified, case crossover study. BMJ 2019; 367 :l6258

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