One study says air pollution played a role in the early COVID-19 outbreak in the United States
Exposure to particulates – a mixture of liquid and solid particles suspended in air, ranging from dust to the transmission of virus droplets into the air – has been harmful to human health. Research by Maria de Fatima Andrade from the University of São Paulo in Brazil found that particulate matter plays an important role in the increase in coronavirus cases in cities.
The authors write:
“The results support the virus transport hypothesis, which means that the virus can synergistically associate with the particles already present in the air. We conclude that PM2.5 plays a small but noticeable role in COVID-19 transmission.”
The study “Investigating the Short-Term Role of Particles in the COVID-19 Outbreak in Cities in the US” is available as a preprint on the medRxiv * server while the article is being peer-reviewed.
Analysis of COVID-19 case data and pollution levels
The researchers examined the short-term relationships between particles and how they contributed to COVID-19 cases in US cities in the early stages of the pandemic.
They collected pollutant information from December 30, 2019 through July 31, 2020 using multiple data sets including the World Air Quality Index project and John Hopkins University’s 2019 novel coronavirus COVID-19 (2019-nCoV) data repository. You have compared the city-level pollution data from both data sets with the COVID-19 data for the district. The team then limited their data analysis to cities where at least 80% of the data was available after the first case and at least 70% of the data contained particles less than 1 µg for PM and nitrogen dioxide and 1 ppm for carbon monoxide.
The researchers analyzed particle concentrations of less than 2.5 µm and between 10 and 2.5 µm ((PM2.5 and PM10, respectively).
A Granger causality analysis was used to identify possible associations between current pollution levels and the rate of daily COVID-19 cases in cities. They also used a logistic adjustment curve to measure the number of accumulated COVID-19 cases. Delayed correlations were used to find a relationship between the accumulated cases and the influence of pollution on the spread of Severe Acute Respiratory Syndrome (SARS-CoV-2).
Spatial distribution of the Granger causal test between pollutant concentrations and new cases of COVID-19 in US states. Counties where the Granger F test p-values are green when they are below 0.05 and pink when above. Dark gray squares were drawn around colored districts around the visualization.
What they found
The results showed that PM2.5 levels were associated with COVID-19 cases in 17 out of 44 cities. PM2.5 was significantly higher from 0 to 18 days. Higher delays were consistent with the incubation period for SARS-CoV-2, suggesting that a PM2.5 concentration significantly affected outbreak development.
The researchers conclude that PM2.5 is a major contributor to the coronavirus outbreak. They found that this concentration of particulates increased the rate of COVID-19 cases in cities by 67%. This correlation was not observed with PM10.
Based on the results, the researchers propose several explanations:
“We can describe at least three possible mechanisms underlying these relationships: (1) long-term PM2.5 exposure increases vulnerability of the population; (2) PM2.5 indicates social mobility, and (3) PM2.5 is a viral transport mediator in the air. Mechanisms 1 and 2 are disruptive factors for mechanism 3. “
Other pollutants like PM10 and nitrogen dioxide have also been linked to new COVID-19 cases, but in fewer cities. Nitrogen dioxide has been linked to the rate of COVID-19 cases in 7 out of 28 cities and PM10 in 8 out of 20 cities.
Carbon monoxide was significantly linked to the rate of COVID-19 cases in 4 out of 21 locations. Carbon monoxide also correlated with accumulated fall rates with significantly higher correlations after 26 days.
No pattern was found of how the new COVID-19 cases spread across cities, indicating possible confusing effects such as weather and other unique regional features.
Given the diverse geographic landscape of the United States and different government interventions during the pandemic, the researchers suggest that the results may be generalizable to other countries. They say that with more COVID-19 data, future studies would focus on the relationship between pollution levels and COVD-19 cases in cities around the world.
“By and large, we hope to raise the interest of the scientific community, public awareness and decision-makers about the potential synergies between virus transmission and air pollution,” the research team wrote.
On actionable points, the team says any attempt to reduce the spread of COVID-19 cases in cities would help end the pandemic.
* Important NOTE
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and should therefore not be considered conclusive, guide clinical practice / health-related behavior, or be treated as established information.