1. Introduction
Several studies reported an overall decrease in the number of Pediatric
Emergency Department (PED) admissions in 2020 during lockdown periods
related to social measures adopted to limit spreading of SARS-CoV-2
pandemic, including a marked reduction of asthma
referrals1,2. This led to a growing interest in
determining to what extent these life-style changes might have
influenced asthma triggers3–5.
Asthma is a multi-factorial airways disease: in predisposed people,
exposure to respiratory infections, air pollution and allergens may
trigger asthma exacerbations6,7. Infections are the
main triggers of acute bronchospasm in children of any age, especially
in the preschoolers8,9. Sensitization to environmental
allergens, such as pollen, is reported as a further important risk
factor for the development of asthma exacerbations10.
Regarding the role of air pollution, most studies reported how
particulate matter smaller than 2.5 microns and 10 microns
(PM2.5, PM10) and the co-emitted gaseous
pollutants (NO, NO2, O3) can induce
airway inflammation, hyper-responsiveness and oxidative injury to the
airways, which can lead to asthma11. However, even if
the international air quality standards for atmospheric particulate
matter (PM) are based on total mass concentrations, the World Health
Organization (WHO) acknowledges that not every PM chemical component is
equally important in causing airways disease12.
Research on this issue is mostly focused on traffic-related air
pollution (TRAP) and has provided evidence of the links between adverse
health effects and PM chemical composition11,13–15.
Urban anthropogenic PM presents a three-fold higher oxidative potential
per unit of PM mass concentration than rural PM16.
In this observational retrospective cross-sectional study, we aimed to
identify how asthma-related referrals in children were affected by the
restrictive measures during the entire 2020, in relation to the main
features of potentially associated environmental triggers, i.e. air
pollution and pollen. The selected urban area of Bologna, in Northern
Italy, represents an important population basin of about 400000
inhabitants and can be considered an ideal setting for this study as it
is one of the areas more dramatically hit by the pandemic, and also
well-known for a high prevalence of respiratory disease and for being
one of the main air quality European hotspot, characterized by PM levels
well above the limit set by the European Air Quality Directive and by
the WHO.