Air pollution linked to higher risk of severe Covid-19: Study

Long-term exposure to air pollution is associated with a greater risk of severe Covid-19, according to a study conducted in Germany.

The study, presented at the annual meeting of the European Society of Anaesthesiology and Intensive Care in Milan, Italy from June 4-6, found that people living in counties with higher nitrogen dioxide (NO2) levels were more likely to need ICU care and mechanical ventilation if they had Covid-19.

The researchers noted that long-term exposure to NO2, a gas released into the atmosphere when fossil fuels are burned, can have harmful effects on the lungs.

This includes damage to the endothelial cells, which play a key role in the transfer of oxygen from inhaled air to the blood.

The research team led by Susanne Koch, from Charitr - Universitatsmedizin Berlin in Germany explored the impact of long-term air pollution on the need for ICU treatment and mechanical ventilation of Covid-19 patients.

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They used air pollution data from 2010 to 2019 to calculate the long-term annual mean level of NO2 for each county in Germany.

This ranged from 4.6 microgrammes per cubic metre (µg/m3) to 32 µg/m3, with the highest level in Frankfurt and the lowest level in Suhl.

"Long-term exposure to NO2 long before the pandemic may have made people more vulnerable to more severe Covid-19 disease," said Koch.

"Exposure to ambient air pollution can contribute a range of other conditions, including heart attacks, strokes, asthma and lung cancer and will continue to harm health long after the Covid-19 pandemic ends," the scientist said.

The German Interdisciplinary Association for Intensive Care and Emergency Medicine (DIVI) registry, which was set up to monitor ICU capacity during the pandemic, was used to provide information on how many Covid-19 patients in each hospital needed ICU treatment and mechanical ventilation.

The study period was from April 16 2020, when the reporting of data to the DIVI registry became mandatory, to May 16 2020, when lockdown restrictions were lifted. 392 out of Germany's 402 counties were included in the analysis.

Demographic factors such as population density and age and sex distribution, socio-economic factors and health parameters, including pre-existing health conditions which can affect Covid-19 severity, were all adjusted for.

The study found that there was a greater need for ICU treatment and mechanical ventilation of Covid-19 patients in counties with higher long-term annual mean NO2 levels.

Each 1 µg/m3 increase in long-term annual mean NO2 concentration was associated with a 3.2 per cent increase in the number of ICU beds occupied by Covid-19 patients and a 3.5 per cent increase in the number of Covid-19 patients who needed mechanical ventilation.

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On average, 28 ICU beds and 19 ventilators were needed for Covid-19 patients in each of the ten counties with the lowest long-term NO2 exposure, during the month studied, the researchers said.

This compares to an average of 144 ICU beds and 102 ventilators in the ten counties with the highest long-term NO2 exposure, they said.

The researchers said that while their results do not prove causation, there is a potential biological explanation for them.

ACE-2, the protein that the Covid-19 virus binds to when entering our cells, has many key roles in the body, including helping regulate the activities of angiotensin II, a protein which increases inflammation.

On the other hand, ACE-2 helps "put the brakes" on inflammation. When the SARS-CoV-2 virus binds to ACE-2, however, these brakes are removed, the researchers said.

Air pollution also "releases the brakes" and so the combination of Covid-19 and long-term air pollution exposure could lead to more severe inflammation and more severe Covid-19, according to the researchers.

Although the links between air pollution and Covid-19 have been analysed before, few studies have focused on severity of disease or taken into account population density, underlying health conditions and other factors which affect the impact of the disease.

The findings are in line with other recent studies which have linked long-term NO2 exposure with a higher Covid-19 incidence and a higher fatality rate, the researchers added.