Assessment of the SARS-CoV-2 basic reproduction number, R0, based on the early phase of COVID-19 outbreak in Italy

As of March 12^th Italy has the largest number of SARS-CoV-2 cases in Europe as well as outside China. The infections, first limited in Northern Italy, have eventually spread to all other regions. When controlling an emerging outbreak of an infectious disease it is essential to know the key epidemiological parameters, such as the basic reproduction number <i>R</i> ₀, i.e. the average number of secondary infections caused by one infected individual during his/her entire infectious period at the start of an outbreak. Previous work has been limited to the assessment of <i>R</i> ₀ analyzing data from the Wuhan region or Mainland China. In the present study the <i>R</i> ₀ value for SARS-CoV-2 was assessed analyzing data derived from the early phase of the outbreak in Italy. In particular, the spread of SARS-CoV-2 was analyzed in 9 cities (those with the largest number of infections) fitting the well-established SIR-model to available data in the interval between February 25-March 12, 2020. The findings of this study suggest that <i>R</i> ₀ values associated with the Italian outbreak may range from 2.43 to 3.10, confirming previous evidence in the literature reporting similar <i>R</i> ₀ values for SARS-CoV-2.