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URL: https://pubmed.ncbi.nlm.nih.gov/32973066/

⇱ Potential role of particulate matter in the spreading of COVID-19 in Northern Italy: first observational study based on initial epidemic diffusion - PubMed

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Abstract

Objectives: A number of studies have shown that the airborne transmission route could spread some viruses over a distance of 2 meters from an infected person. An epidemic model based only on respiratory droplets and close contact could not fully explain the regional differences in the spread of COVID-19 in Italy. On March 16th 2020, we presented a position paper proposing a research hypothesis concerning the association between higher mortality rates due to COVID-19 observed in Northern Italy and average concentrations of PM10 exceeding a daily limit of 50 µg/m3.

Methods: To monitor the spreading of COVID-19 in Italy from February 24th to March 13th (the date of the Italian lockdown), official daily data for PM10 levels were collected from all Italian provinces between February 9th and February 29th, taking into account the maximum lag period (14 days) between the infection and diagnosis. In addition to the number of exceedances of the daily limit value of PM10, we also considered population data and daily travelling information for each province.

Results: Exceedance of the daily limit value of PM10 appears to be a significant predictor of infection in univariate analyses (p<0.001). Less polluted provinces had a median of 0.03 infections over 1000 residents, while the most polluted provinces showed a median of 0.26 cases. Thirty-nine out of 41 Northern Italian provinces resulted in the category with the highest PM10 levels, while 62 out of 66 Southern provinces presented low PM10 concentrations (p<0.001). In Milan, the average growth rate before the lockdown was significantly higher than in Rome (0.34 vs 0.27 per day, with a doubling time of 2.0 days vs 2.6, respectively), thus suggesting a basic reproductive number R0>6.0, comparable with the highest values estimated for China.

Conclusion: A significant association has been found between the geographical distribution of daily PM10 exceedances and the initial spreading of COVID-19 in the 110 Italian provinces.

Keywords: epidemiology; public health; virology.

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Conflict of interest statement

Competing interests: None declared.

Figures

👁 Figure 1
Figure 1
(A) Average daily exceedances of PM10 versus number of monitoring stations in different Italian provinces from February 9th to February 29th, 2020. (B–E) Spreading of COVID-19 infections (officially confirmed cases) during the period March 3rd to March 13th, 2020.
👁 Figure 2
Figure 2
(A) Daily new COVID-19 infections in Italy from February 24th to April 4th 2020. (B) Trend of COVID-19 spread in Italy during the first 15 days of the epidemic.
👁 Figure 3
Figure 3
Relationship between the daily limit value of exceedances of PM10 and COVID-19 case ratios over the population in Italian provinces. (A) Scatter plot on a semilogarithmic scale relating the proportion of COVID-19 cases of the population of northern (grey squares) and southern (black bullets) Italian provinces vs the average daily limit value of exceedances of PM10. The dashed binomial (logistic) regression is characterised by an increasing slope of 0.25 (p<0.001). (B) Box plots showing that—with a 1.29 cut-off value of exceedance of PM10—the proportion of COVID-19 cases is greater (p<0.001) in the most polluted provinces (39 out of 41 located in Northern Italy) than the less polluted provinces, mainly located in Southern Italy (62 out of 66). (C) Box plots showing that even considering PM2.5 exceedance rates (despite 39% missing data due to the absence of monitoring stations for PM2.5) the proportion of COVID-19 in Po Valley might be stratified consistently (p<0.001) with PM10 data presented in figure 1B–E.
👁 Figure 4
Figure 4
(A) Trends of COVID-19 spread in Milan and Rome during the first 14 days of the epidemic; the starting date in Milan is February 25th and could correspond to infections acquired by February 8th that became clinically evident or detectable within the subsequent 17 days (lag period between the infection and diagnosis). (B) Distribution of the average daily PM10 exceedances in Rome and Milan on February 2020.
👁 Figure 5
Figure 5
Scheme of possible enhancement of viral transmission through stabilised human exhalation on particulate matter (PM).

References

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