A possible link between long-term exposure to air pollution and the severity of coronavirus infections has been found.

The study, published by Environmental Health Perspectives, was conducted by scientists at the Barcelona Institute for Global Health and examined the outcomes of 9605 adult participants from Catalonia.

Most of the participants were sourced from pre-existing study cohorts, the largest of which was the Genomes for Life cohort, numbering almost 9000, and taking in participants between the ages of 40 and 65.

The study began in late May, following Spain’s first confirmed infection in February and its first lockdown in March.

4103 blood samples were collected from a randomly selected sample of the participants and processed within 24 hours of collection for levels of antibodies.

Blood samples were taken to establish levels of infection and antibody response among those infected, as well as to help the researchers to identify participants who had had asymptomatic cases of the virus.

Cases of infection were recorded by either self-reported hospital admission, positive diagnostic test, or more than three self-reported COVID-19 symptoms after contact with a COVID-19 case.

The study found that those who were exposed to moderate to high levels of air pollution were found to be 51% more likely to have suffered a severe case of COVID-19 and be subsequently hospitalized.

Among the limitations of the study noted by the researchers are the fairly narrow age range of the majority of participants, including few young or elderly adults, and the small number of confirmed infections among the cohort, thus making data collection an imperfect process.

Though the study found that air pollution levels were not statistically significantly associated with rates of infection, scientists expect the increased severity follows pre-existing damage to people’s immune systems caused by high levels of pollution.