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 up to 16.6%.
After analyzing data for 355 Dutch municipalities, the study found that an increase in fine particulate matter concentrations of 1 microgram per cubic meter was linked with an increase of up to 15 COVID-19 cases, four hospital admissions, and three deaths.
The first confirmed COVID-19 case in the Netherlands occurred in late February and by late June over 50,000 cases had been identified. The national spread of COVID-19 cases shows a greater number in the south-eastern regions.
Unusually, these hotspots of disease transmission are in relatively rural regions where there are fewer people living close together. The Dutch media offered one potential explanation. In late February and early March each year, these areas hold carnival celebrations that attract thousands of people to street parties and parades – 2020 was no exception, so does that explain the rapid spread of COVID-19 there?
While it’s likely that the carnival celebrations played a role, the pattern of cases across these regions suggests other factors may be at least as important.
The south-eastern provinces of North Brabant and Limburg house over 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 particulate matter in air pollution. Concentrations of this are at their highest in air samples from the south-east of the Netherlands.
The correlation between these indicators of air pollution and cases of COVID-19 is clear to see, but is it just a coincidence?
The analysis used COVID-19 data up to 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 the results in context, the highest annual average concentration of fine particulate matter 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 level of the least polluted, the results suggest this would lead to 82 fewer disease cases, 24 fewer hospital admissions, and 19 fewer deaths, purely as a result of the change in pollution.
The correlation found between exposure to air pollution and COVID-19 is not simply a result of disease cases being clustered in large cities where pollution may be higher. After all, COVID-19 hotspots in the Netherlands were in relatively rural regions. Still, region-level data can only get us so far. Within regions, pollution levels and COVID-19 cases can vary considerably from place to place, making it hard to estimate the precise relationship between the two.
Being able to study this link among individual people would allow to more precisely eliminate the influence of age and health conditions. But until this kind of data is available, the evidence of a relationship between pollution and COVID-19 can never be conclusive.
Image source: http://ftp.iza.org/dp13367.pdf