  When an infectious disease strikes a population, the number of newly reported
cases is often the only available information that one can obtain during early
stages of the outbreak. An important goal of early outbreak analysis is to
obtain a reliable estimate for the basic reproduction number, $R_{0}$, from the
limited information available. We present a novel method that enables us to
make a reliable real-time estimate of the reproduction number at a much earlier
stage compared to other available methods. Our method takes into account the
possibility that a disease has a wide distribution of infectious period and
that the degree distribution of the contact network is heterogeneous. We
validate our analytical framework with numerical simulations.
