4. Discussion
Our findings show that in 2020, during the first and second outbreak of
SARS-CoV-2 across Northern Italy, overall childhood asthma exacerbations
were inhibited, as compared to the same calendar period of the previous
5 years: during lockdown-1, PED referrals incurred a significant decline
by 85%, and in the following months by 80%, reflecting the slow,
although incomplete return to almost regular activities during summer.
An increase in PED referrals for acute asthma re-started in August,
continued in September, with a peak in October, anticipating the
so-called “September asthma epidemics”, the common burst of
exacerbations generally observed with the start of the school year and
due to a combination of infectious, allergic, environmental, and
climatic triggers23. The peak in October was less
pronounced than the previous years and this decreasing trend continued
in November and December, when only 8 asthma referrals were registered,
likely reflecting the strict hygiene measures and social distancing
adopted as a consequence of lockdown-2. We also observed a prevalent
reduction trend of hospital admissions and short-stay observations
during the pandemic.
Our PED and many others, reported a substantial activity decrease by ca.
70-80% during lockdown-1, with drastic reductions in referrals for a
wide spectrum of diagnoses1,2. In other studies, this
was attributed to the introduction of new guidance for primary care
(e.g. phone selection triage procedure, more tele-health) and fear of
exposure to SARS-CoV-2 infection, leading to higher risk of severe
illness from delayed diagnosis1,2,24. In contrast, the
reduction of PED referrals for asthma exacerbations was associated with
a significant reduction by 50-60% of high-priority cases, thus, the
reluctance to seek hospital care cannot be the only explanation. A major
role is likely played by a combination of factors.
As reported in other studies, social distancing and stepped-up hygiene
measures determined a concomitant reduction in the diffusion of
respiratory pathogens, leading to decreased respiratory tract
infections3,25–27. Moreover, the feeling of the
emergency period might have enhanced adherence to controller medications
among asthmatic population27,28.
In addition, the reduced exposure to environmental factors – i.e. air
pollution and pollen - may have played a role in the “anomalous”
pattern of asthma exacerbations in 2020. With regard to changes in air
quality during the pandemic, the gaseous pollutants NO2and C6H6, generally associated with
fossil fuel combustion and directly correlated with vehicular traffic in
urban context, showed substantially decreased concentrations during
lockdown periods. In densely populated areas, this clearly mirrored a
reduction of traffic-related sources in concomitance with the
restrictive measures, consistent with observations at a larger scale in
Italy and mobility drop of 75%29.
Unlike NO2 and C6H6, PM
mass concentration was not significantly affected by lockdown measures.
This can be explained by the complex emission patterns of PM in
urbanized environment, encompassing both natural and anthropogenic,
primary and secondary sources, thus leading to mass concentrations
driven to a large extent by non-urban and non-traffic
sources20. By contrast, a substantial reduction in the
contribution of specific chemical components of traffic-related PM was
clearly shown during lockdown-1, i.e. black carbon (BC) and the TRAP
contribution tracer.
It is worth noting that traffic-related PM may gain relevance per unit
mass of PM because of its higher oxidative potential and smaller size,
leading to deposition in the deepest tracts of respiratory
system16. Thus, these observations point to PM less
enriched in ultrafine particles and those co-emitted components and
micropollutants (e.g. BC, heavy metals and polycyclic aromatic
hydrocarbons), which are recognized as specific asthma triggers, able to
drive a cascade of pro-inflammatory and oxidative responses that
increase the risks of acute pulmonary diseases30. This
effect was likely amplified by less time spent outdoor and less
movements during traffic rush-hours, reducing risk associated with
proximity of children to strong local sources (exhaust and non-exhaust
vehicular traffic). Moreover, a higher impact is expected in inner-city
urban areas, where vehicular traffic presents a higher share of
emissions. This evidence would suggest the recommendation for adopting
more specific chemical tracers as air quality indicators, to elucidate
associations between air pollution and respiratory diseases, despite the
commonly used PM mass concentration.
On the contrary, pollen emissions are not impacted by changes in human
behaviors and social restrictions, deriving from known natural sources.
Indeed, during lockdown periods, pollen emissions did not present
substantial variations beyond their interannual variability. However,
the restrictive measures likely influenced exposure profiles of children
in other ways, such as by reducing exposure to outdoor seasonal
allergens.
In conclusion, several factors may explain the substantial decrease in
the number of acute asthma PED referrals during the SARS-CoV-2 pandemic
in 2020, with the concomitant reduction of high-priority codes. The
restrictive measures adopted to limit the pandemic entailed a reduced
exposure to viruses, outdoor environmental allergens, and air pollution,
the latter notably exhibiting weakened inflammatory/oxidative
properties.
Further investigations are needed to clarify in a more quantitative
manner the role of each confounding trigger, driving synergistically
variation in the clinical course of asthma. However, due to the
peculiarity of the lockdown periods, which acted as a big experiment of
anthropogenic air pollution cleansing and radical changes of human
lifestyle, this study represented a unique opportunity to observe these
hypotheses using real data from a severely SARS-CoV-2 affected urban
area, reflecting what occurred in many densely populated areas around
the world.