Do Air Pollution Levels Influence COVID-19 Mortality Risk?

While the world has focused its full attention on the current coronavirus outbreak, other issues we were concerned about regarding our health might currently seem almost irrelevant to many of us. However, there is one factor that shouldn’t be ignored – potentially not even when looking at survival rates of COVID-19: air pollution.

While it is too early to clearly analyse the factors that affect survival rates of COVID-19 in different regions of the world, there is a fair amount of evidence that promotes the hypothesis that air pollution levels could play a significant role.

Long-term effects of air pollution are likely to increase COVID-19 mortality risk

It is well understood that long-term exposure to air pollution can damage our lungs and cardio-vascular system and increase our risk of developing or exacerbating chronic diseases such as asthma, COPD, cardiovascular disease or diabetes. Studies have further shown that long-term exposure to air pollutants such as nitrogen dioxide, particulate matter and ozone can cause damages to the respiratory system that limits its ability to fight common respiratory infections such as the flu or pneumonia (Anoop et al., 2003, Neupane et al, 2010). Air pollutants trigger the lungs’ defence system and activate immune cells to remove the pollutants. On the long term, this is causing inflammatory processes in the lungs that make it easier for viruses or bacteria to enter. People who have been exposed to high air pollution levels for a year or more are more susceptible to get pneumonia, and if they get it, they are also more likely to die from it.

Experts think that it is plausible that the same is true for Covid-19. For the Middle East respiratory syndrome (MERS), a respiratory disease caused by another virus from the coronavirus family, smokers were more than twice as likely to die from the disease as non-smokers (Nam et al, 2017). Furthermore, during the 2002/2003 SARS outbreak, people who lived in cities with high air pollution levels experienced mortality rates twice as high compared to cities with moderate pollution levels (Cui et al., 2003).

Short-term effects of air pollution on the course of COVID-19

A more important question when considering implications for managing the current pandemic is whether the susceptibility to the virus or the course of disease could already be affected by exposure to short episodes of high pollution. If that was the case, keeping air pollution low now, especially around vulnerable groups or COVID-19 patients would be one factor that could help reduce the impact of the pandemic. Looking at the scientific literature, there is evidence that at least for vulnerable groups, short-term pollution exposure can affect disease severity of respiratory infections. Especially short episodes of high fine particulate matter concentrations are associated with an increased number of hospitalisations due to pneumonia and also increased mortality due to pneumonia (Pirozzi et al, 2017).

Finally, there is also some evidence that fine particulate matter could serve as a vector for the virus. By binding to the particles, viruses could travel and survive for much longer and therefore infect more people than in a low pollution environment (Chen et al., 2017).

Fortunately cleaning up the air is already a side effect of the current containment measures. On Twitter, people all over the world are writing and posting pictures amazed by how clean and fresh the air is after a few days of lockdown.

Recommendations

For healthcare providers and anyone who wants to manage their health a bit better these days, there are a few recommendations that certainly would not harm to embrace:

Reduction of indoor air pollution. Cleaning agents, cooking and pollutants emitted from furniture or carpets can cause harmful levels of air pollution in your home or working place. Widely opening all windows for a few minutes several times a day can drastically reduce exposure to harmful indoor pollutants. If you live next to a lot of traffic, try keeping your windows closed during peak traffic hours.

Avoid high outdoor air pollution episodes. While many air pollutant concentrations might be down due to lockdown measures, some pollutants, such as particulate matter, have many different sources. They are highly dependent on weather conditions and can be influenced by long-range transport from other regions. So keeping an eye on daily air pollution levels or forecasts can help to plan ahead to minimise exposure to high pollution levels.

As COVID-19 might not just go away tomorrow, but could likely become something that will continue to threaten us in the future there is now one more reason for cities to put a priority on cleaning up the air we breathe.

Sources:

Chen, G., Zhang, W., Li, S., Zhang, Y., Williams, G., Huxley, R., … & Guo, Y. (2017). The impact of ambient fine particles on influenza transmission and the modification effects of temperature in China: a multi-city study. Environment international, 98, 82-88.

Chauhan, A. J., & Johnston, S. L. (2003). Air pollution and infection in respiratory illness. British medical bulletin, 68(1), 95-112.

Cui, Y., Zhang, Z. F., Froines, J., Zhao, J., Wang, H., Yu, S. Z., & Detels, R. (2003). Air pollution and case fatality of SARS in the People’s Republic of China: an ecologic study. Environmental Health, 2(1), 15.

Nam, H. S., Park, J. W., Ki, M., Yeon, M. Y., Kim, J., & Kim, S. W. (2017). High fatality rates and associated factors in two hospital outbreaks of MERS in Daejeon, the Republic of Korea. International Journal of Infectious Diseases, 58, 37-42.

Neupane B et al. Long-term exposure to ambient air pollution and risk of hospitalization with community-acquired pneumonia in older adults. Am J Respir Crit Care Med 2010 Jan 1; 181:47.

Pirozzi, C. S., Jones, B. E., VanDerslice, J. A., Zhang, Y., Paine III, R., & Dean, N. C. (2018). Short-term air pollution and incident pneumonia. A case-crossover study. Annals of the American Thoracic Society, 15(4), 449-459.

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