Are rising lower respiratory infection hospital admissions linked to dirty air?

The Covid crisis highlighted gaps in our understanding of the role that air pollution plays in infections.

A flurry of studies carried out during and after the crisis allowed a UK government advisory group to conclude that long-term exposure to air pollution may contribute to worse coronavirus symptoms. The group offered examples that included a study of more than 3 million people in Denmark that showed air pollution added to the risk of death or hospital admission with severe Covid, especially in the least well off.

Now a study led by the Barcelona Institute for Global Health has examined whether long-term exposure to air pollution is a factor in hospital admissions for lower respiratory infections (LRIs). LRIs include chest infections, pneumonia and bronchitis and place a large and increasing burden on health services. Alone, they accounted for a 15% increase in the rate of hospital admissions in the UK between 1999 and 2019.

Prof Cathryn Tonne, who led the study, said: “We have so much evidence of the negative health effects of air pollution on a wide range of health outcomes. We were surprised to see how limited the evidence still was for air pollution and LRIs in adults.”

Nearly 4 million adults in Catalonia were studied over a five-year period. During this time, 94,000 people were admitted to hospital with LRIs – almost 60,000 of these had flu or pneumonia. Their health records were then compared with air pollution in their neighbourhoods. People over 65, and especially men with blood pressure problems, were most vulnerable to needing hospital admission with an LRI that was worsened by air pollution. This included particle pollution and exposure to nitrogen dioxide, a pollutant from diesel exhaust and burning fossil gas. Men living in the most polluted 25% of neighbourhoods had a 50% increased chance of being admitted to hospital with these infections compared with those in cleaner areas, but even here the risk was not zero.

Tonne said: “Importantly, we also observed positive associations between air pollution and hospital admission for LRI even at relatively low pollution concentrations. Continuing to reduce air pollution will have broad health benefits. This includes reducing the risk of hospital admission for common respiratory infections, particularly among vulnerable people.”

In 2022, Prof Sir Stephen Holgate chaired an inquiry by the UK Academy of Medical Sciences into the health burden from respiratory infections that the UK experiences each winter. Commenting on the study from Catalonia, Holgate said: “It is known that air pollution episodes trigger hospital admissions for serious lung infections. This study of nearly 4 million people clearly shows that long-term exposure to outdoor particulate pollution and nitrogen dioxide also drives infection-related hospital admissions.

“This happens even at levels below the World Health Organization-related limit values [and] surely means we must now insist upon stricter air quality standards to protect vulnerable people.”