London, Nov 18 (IANS): People infected with Covid, who had long-term exposure to air pollution, are more likely to end up in hospital or intensive care, finds a study.

The study found an association between higher exposure to Nitrogen Dioxide (NO2) and fine particulate matter (PM2.5) and increased disease symptoms, particularly for severe cases that ended in the hospital or in intensive care.

The association with PM2.5 was stronger for men over 60 years of age and people living in socioeconomically deprived areas, said the researchers from Barcelona Institute of Global Health (ISGlobal).

A series of previous studies have suggested that regions with higher pre-pandemic levels of air pollution had a higher incidence of Covid-19 cases and deaths. However, the reasons for these associations are not yet clear; air pollution could favour airborne transmission of the virus, or it could increase an individual's susceptibility to infection or disease.

"The problem is that previous studies were based on reported cases, which had been diagnosed, but missed all the asymptomatic or undiagnosed cases," said first author Manolis Kogevinas, researcher at ISGlobal.

To understand, the team measured a series of virus-specific antibodies in a cohort of adults living in Catalonia, with information on the long-term exposure of such individuals to air pollutants (NO2, PM2.5, black carbon and ozone).

The study, published in Environment Health Perspectives, included 9,605 participants among which there were 481 confirmed cases (5 per cent). In addition, blood samples from over 4,000 participants were taken to determine the presence and quantity of IgM, IgA and IgG antibodies to five viral antigens.

Of these, 18 per cent had virus-specific antibodies, but no association was found between infection and exposure to air pollutants. However, among those who were seropositive (that is, got infected), an association was found between higher exposure to NO2 and PM2.5 and higher levels of IgG specific for the five viral antigens -- an indication of higher viral burden and/or symptom severity.

"Our study provides the strongest evidence globally on the association of ambient air pollution and Covid-19," said Kogevinas. "These results are in line with the association between air pollution and hospitalisation described for other respiratory diseases such as influenza or pneumonia".

Further, air pollution can also contribute by favouring the development of cardiovascular, respiratory or other chronic conditions, which in turn increase the risk of severe Covid-19.

The team said that the results provide additional support for the public health benefits of reducing air pollution levels, and highlight the influence of environmental factors on infectious diseases.