The global death toll for COVID-19 has now exceeded half a million. To slow the spread of the disease, we must better understand why some places have more cases and deaths than others.
One factor that may partially explain this is air pollution. Research has shown that long-term exposure to pollutants such as fine particles (often called PM2.5 since they are particles smaller than 2.5 microns), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) can reduce the lung function and cause respiratory diseases. . These contaminants have also been shown to cause a persistent inflammatory response even in the relatively young and to increase the risk of infection by viruses that attack the respiratory tract.
The pathogen that causes COVID-19 – SARS-CoV-2 – is one of those viruses. Several studies have already suggested that poor air quality can leave people at higher risk for contracting the virus and at higher risk for serious illness and death. A study from the US found that even a small increase in PM2.5 concentrations of 1 microgram per cubic meter is associated with an 8% increase in the death rate of COVID-19. Our new research looked at the relationship between COVID-19 cases and exposure to air pollution in the Netherlands and found that the equivalent figure for that country could be as high as 16.6%.
Read more: What you need to know about how the coronavirus is changing science
The unusual case of the Netherlands
After analyzing data from 355 Dutch municipalities, we found that an increase in fine particle concentrations of 1 microgram per cubic meter was associated with an increase of up to 15 cases of COVID-19, four hospital admissions, and three deaths.
The first confirmed case of COVID-19 in the Netherlands occurred in late February and by the end of June more than 50,000 cases had been identified. The national spread of COVID-19 cases shows a higher number in the southeastern regions.
Matt Cole, Author provided
Unusually, these critical points of disease transmission are found in relatively rural regions where fewer people are living together. The Dutch media offered a possible explanation. In late February and early March of each year, these areas hold carnival celebrations that draw thousands of people to street parties and parades. 2020 was no exception, so does that explain the rapid spread of COVID-19 there?
While carnival celebrations likely played an important role, the pattern of cases in these regions suggests that other factors may be at least as important.
The southeastern provinces of North Brabant and Limburg are home to more than 63% of the country’s 12 million pigs and 42% of its 101 million chickens. Intensive livestock production produces large amounts of ammonia. These particles often form a significant proportion of fine particles in air pollution. Concentrations of this are highest in air samples from the southeastern Netherlands.
The correlation between these air pollution indicators and COVID-19 cases is clear, but is it just a coincidence?
EPA-EFE / MARCEL VAN HOORN
Contaminants associated with COVID-19
Our analysis used COVID-19 data as of June 5, 2020, capturing almost the entire known course of the Dutch epidemic. The relationship we found between pollution and COVID-19 exists even after controlling for other contributing factors, such as carnival, age, health, income, population density, and others.
To put our results in context, the highest average annual concentration of fine particles in a Dutch municipality is 12.3 micrograms per cubic meter, while the lowest is 6.9. If concentrations in the most polluted municipality fell to the least polluted level, our results suggest that this would lead to 82 fewer cases of illness, 24 fewer hospital admissions, and 19 fewer deaths, simply as a result of the change in pollution.
Read more: What we do and don’t know about the links between air pollution and the coronavirus
The correlation we found between exposure to air pollution and COVID-19 is not simply the result of the accumulation of disease cases in large cities where pollution may be higher. After all, the hot spots for COVID-19 in the Netherlands were in relatively rural regions. Still, data at the region level can only go so far. Within regions, levels of contamination and COVID-19 cases can vary considerably from place to place, making it difficult to estimate the precise relationship between the two.
Being able to study this link between individual people would allow us to more precisely eliminate the influence of age and health conditions. But until this type of data is available, the evidence for a relationship between contamination and COVID-19 can never be conclusive.
