Analisi dell’epidemia di COVID-19 in Italia attraverso il modello Reed-Frost. Una metodologia per delimitare nel tempo le ondate epidemiche

[Autom. eng. transl.] Introduction An epidemic wave can be defined as that period between a significant and lasting increase in the number of disease cases and a significant and lasting decrease in them. Delimiting epidemic waves in a defined space over time can help study epidemic phenomena in different contexts, promoting analysis and comparisons, while at the same time proving to be a valuable support for the decision making process in public health. Based on the Reed-Frost SIR model, which is based on the concept of effective contact probability (probability of contact between infected people and susceptible people leading to the transmission of the infection), an accessible and reproducible methodology is proposed to determine the dates of the beginning and end of epidemic waves. Materials and methods Epidemic data published by the Civil Protection from 24 February 2020 to 16 February 2022 were used to collect information on the COVID-19 epidemic in Italy. The Reed-Frost model and the logic of tertiles of values ​​were applied to develop a methodology based on the calculation of the probability of effective contact: the maximum values ​​of probability of effective contact were used to identify the beginning of the waves, minimum values ​​for identify the end of the waves and, finally, intermediate values ​​of probability of effective contact were used to identify the peak/inter-wave periods. Results An iterative methodology was developed which led to the identification of the start, end and inter-wave periods and the initial and final days of the COVID-19 epidemic waves in Italy: the first wave from February 26 ± 2 2020 to 28 ± 2 June 2020; the second wave from 1 ± 2 October 2020 to 5 ± 2 July 2021 (with two peaks: 21 ± 2 December 2020 and 2 ± 2 February 2021); the third wave from 13 ± 2 July 2021 to 26 ± 2 September 2021; the fourth wave from the end of October 2021. Conclusions This study has led to the development of an accessible and reproducible methodology to determine the start and end dates of a wave, starting from the sole number of infected people and susceptible people. The major implications of the method mainly consist in allowing benchmarking and forecasting analyzes of the trend of the epidemic to be carried out to support decision-making processes in public health.