The risk of infection and death from COVID-19 could be associated with a heterogeneous distribution of environmental, socioeconomic and demographic factors. Our objective was to investigate, at a small area level, whether prolonged exposure to air pollutants increased the risk of COVID-19 incidence and death in Catalonia, controlling for socioeconomic and demographic factors.

We use a mixed longitudinal ecological design with the study population made up of small areas in Catalonia for the period from February 25 to May 16, 2020. We estimate generalized linear mixed models in which we control for a wide range of confounding factors, both observed as unobserved, as well as spatial and temporal dependence.

We found that prolonged exposure to nitrogen dioxide (NO2) and, to a lesser extent, particulate matter (PM10) were independent predictors of the spatial spread of COVID-19.

Although it is possible that there are biological mechanisms that explain, at least partially, the association between long-term exposure to air pollutants and COVID-19, we hypothesize that the spatial spread of COVID-19 in Catalonia is attributed to the different ease of contact that some people have, the hosts of the virus. This facility depends on the heterogeneous distribution of variables such as population density, precarious housing and the mobility of its residents, for which exposure to pollutants has been a surrogate.