PM 2.5 Pollution Strongly Predicted COVID-19 Incidence in Four High-Polluted Urbanized Italian Cities during the Pre-Lockdown and Lockdown Periods.

Background: The coronavirus disease in 2019 (COVID-19) heavily hit Italy, one of Europe's most polluted countries. The extent to which PM pollution contributed to COVID-19 diffusion is needing further clarification. We aimed to investigate the particular matter (PM) pollution and its correlation with COVID-19 incidence across four Italian cities: Milan, Rome, Naples, and Salerno, during the pre-lockdown and lockdown periods.
Methods: We performed a comparative analysis followed by correlation and regression analyses of the daily average PM ₁₀ , PM _2.5 concentrations, and COVID-19 incidence across four cities from 1 January 2020 to 8 April 2020, adjusting for several factors, taking a two-week time lag into account.
Results: Milan had significantly higher average daily PM ₁₀ and PM _2.5 levels than Rome, Naples, and Salerno. Rome, Naples, and Salerno maintained safe PM ₁₀ levels. The daily PM _2.5 levels exceeded the legislative standards in all cities during the entire period. PM _2.5 pollution was related to COVID-19 incidence. The PM _2.5 levels and sampling rate were strong predictors of COVID-19 incidence during the pre-lockdown period. The PM _2.5 levels, population's age, and density strongly predicted COVID-19 incidence during lockdown.
Conclusions: Italy serves as a noteworthy paradigm illustrating that PM _2.5 pollution impacts COVID-19 spread. Even in lockdown, PM _2.5 levels negatively impacted COVID-19 incidence.