Correcting the actual reproduction number: a simple method to estimate R(0) from early epidemic growth data.

The basic reproduction number, R(0), a summary measure of the transmission potential of an infectious disease, is estimated from early epidemic growth rate, but a likelihood-based method for the estimation has yet to be developed. The present study corrects the concept of the actual reproduction number, offering a simple framework for estimating R(0) without assuming exponential growth of cases. The proposed method is applied to the HIV epidemic in European countries, yielding R(0) values ranging from 3.60 to 3.74, consistent with those based on the Euler-Lotka equation. The method also permits calculating the expected value of R(0) using a spreadsheet.