COVID-19, air pollution and population density
Dear Editor,
We fully agree with Carminati and co-workers that air pollution is not
the only determinant influencing the incidence and severity of COVID-19.
Individual severity factors have been intensively studied and
reported1. Nevertheless, the review of our data (data
not shown) allows us to confirm that the death rate, even after adjusted
for population density, was higher in the regions of northern as
compared to that of southern Italy2.
More than the geographical population density, it has been suggested
that, in addition to other variables mentioned in our paper, the
population density in confined spaces, such as homes and working places,
may influence the virus spread2,3. However, the high
population density in confined spaces existing in some southern cities,
where many people live in small houses, was still associated with a
lower mortality rate compared to that of northern
cities2.
Therefore, we still think that environmental air pollution represents a
major factor in influencing COVID-19 burden and mortality. Certainly,
although not shown by data collected in the three cities considered by
Carminati and co-workers, the level of air pollutants in northern
Italian cities has unanimously been reported to be significantly higher
than that in southern Italian cities.
On the other hand, the objective of our work was not to confirm the role
of air pollution in COVID-19 – documented by several studies worldwide-
but to suggest a mechanism through which an epithelial damage – also
caused by other offending agents and common in other “epithelial
barrier diseases” – may result in the immune changes typically
associated with severe COVID-194. In accordance with
the epithelial barrier hypothesis, it was recently reported that
bacterial DNA passage to circulation, a marker of epithelial barrier
leakiness in the gut, has been shown to be linked to severe
COVID-195.
Moreover, although recent studies suggest that even a short-term
exposure to pollutants is associated with SARS CoV-2
infection3, chronic exposure has a more relevant role
in influencing incidence and severity of COVID-19 than actual values of
pollutants during the pandemic, possibly influenced by the reduced
vehicle traffic and industrial emissions.
References