Lombardy is characterized by very large urban areas, and ranks among the most polluted areas of Europe due to unfavorable geographical position, climate characteristic, land use, and emission sources ( Carugno et al., 2018). Areas with greater density population, therefore, could be at higher risk of contagion. SARS-CoV-2 infection spreads by human-to-human contact, mainly through respiratory droplets and the contact with contaminated surfaces, although airborne transmission is considered possible in closed environment spaces ( Young et al., 2020). At the same time, the uneven geographical distribution repeated itself also within Lombardy, with the disease clustering in the Provinces of Bergamo, Cremona and Lodi ( Cereda et al., 2020). In the following 20 days, cases in Lombardy rapidly rose, making the region the centre of the Italian Coronavirus Disease 2019 (COVID19) outbreak. On the 20th of February, a man from the Lodi province (southern Lombardy) was the first known confirmed Italian case of infection by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The findings observed suggest that these factors, in particular conditions and lags, may increase individual susceptibility to the development of viral infections such as SARS-CoV-2. In addition, low temperature and low wind speed in some lags resulted associated with increased daily COVID19 incidence. PM 10, PM 2.5 and O 3 concentrations in the last lags seem to be related to an increased COVID19 incidence, probably due to an increased susceptibility of the host. The results did not show a univocal relationship between air quality or climate factors and COVID19 incidence.
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Additionally, change points (Break Points-BP) in the relationship between incident cases and air pollution or climatic factors were estimated. A univariable mixed model with a logarithm transformation as link function was applied for each day, from 15 days (lag15) to one day (lag1) before the day of detected cases, to evaluate the effect of each variable. The daily number of COVID19 cases in Lombardy from February 25th to March 10th, 2020, and the daily average concentrations up to 15 days before the study period of particulate matter (PM 10, PM 2.5), O 3, SO 2, and NO 2 together with climate variables (temperature, relative humidity – RH%, wind speed, precipitation), were analyzed. The study aims to assess the short-term influence of air pollution and climate on COVID19 incidence in Lombardy (Italy), during the early stage of the outbreak, before the implementation of the lockdown measures. Short-term exposure to air pollution, as well as to climate variables have been linked to a higher incidence of respiratory viral diseases.