Modelling and predicting the spatio-temporal spread of COVID-19 in Italy
Abstract Background: Severe acute respiratory syndrome Coronavirus 2019 (COVID-19) has been firstly detected in China at the end of 2019 and it spread in few months all over the world. Italy is the second country in the World for number of cases, and the diffusion of COVID-19 has followed a peculiar spatial pattern. However, the interest of scientific community has been devoted almost exclusively to the prediction of the disease evolution over time so far. Methods: Official freely available data about the number of infected at the finest possible level of spatial areal aggregation (Italian provinces) are used to model the spatio-temporal distribution of COVID-19 infections at local level. An endemic-epidemic time-series mixed-effects generalized linear model for areal disease counts has been implemented to understand and predict spatio-temporal diffusion of the phenomenon. Results: Three subcomponents characterize the fitted model. The first describes the transmission of the illness within provinces; the second accounts for the transmission between nearby provinces; the third is related to the evolution of the disease over time. At the local level, the provinces first concerned by containment measures are those that are not affected by the effects of spatial neighbours. On the other hand, the component accounting for the spatial interaction with surrounding areas is prevalent for provinces that are strongly involved by contagions. Moreover, the proposed model provides good forecasts of the number of infections at local level while controlling for delayed reporting. Conclusions: A strong evidence is found that strict control measures implemented in some provinces efficiently break contagions and limit the spread to nearby areas. While containment policies may potentially be more effective if planned considering the peculiarities of local territories, the effective and homogeneous enforcement of control measures at national level is needed to prevent the disease control being delayed or missed as a whole. This may also apply at international level where, as it is for the EU or the USA, the internal border checks among states have largely been abolished.