Elevated levels of the pollutant PM2.5 in crowded subways of cities with high COVID-19 related mortality-when COVID-19 went underground

Background:Recent literature indicates that the pollutant,particulate matter PM2.5,may have an impact on COVID-19 related infection and mortality.Genes coding for SARS-CoV-2 has been found adherent to PM2.5 and possibly the COVID-19/PM2.5 complex may be involved in the transmission and the exacerbation of COVID-19 infection.PM2.5 levels in deep underground subways have been found up to 90 times higher than roads closer to the surface.Method:The levels of PM2.5 were retrieved from literature assessing particulate matter PM2.5 measured on subway platforms in two groups of cities.These cities were differentiated by the COVID-19 population percentage mortality rate(0.007%vs 0.19%)(P<0.0004).Data regarding the number of stations,length of the networks(km)and the annual ridership were also obtained from literature related to underground commuting.Results:The population percentage mortality related to SARS-CoV-2 infection correlated significantly for both minimum(P<0.01)and maximum(P<0.00001)levels of PM2.5.The cities’subways with low COVID-19 mortality had minimum platform PM2.5 levels of 27.4(SD+/-17.2μg/m3)compared to 63.4μg/m3(SD+/-10.8μg/m3)in cities with high SARS-CoV-2 associated mortality(P<0.01).Subway maximum levels of PM2.5 in cities with low COVID-19 mortality was 53.4μg/m3(SD+/-21.8μg/m3)while that of underground networks with high COVID-19 mortality had maximum platform PM2.5 levels of 172.1μg/m3(SD+/-98μg/m3)(P<0.001).Conclusion:Underground networks may have inherent characteristics accelerating spread of SARSCoV-2 infection and consequent mortality.The highly elevated levels of PM2.5 in overcrowded subways with extensive reach,may have acted as a co-factor to disseminate the pandemic in a number of metropolises.