The transmission of avian influenza between humans is extremely rare, and it mostly affects individuals who are in contact with infected family member. Although this scenario is uncommon, there have been multiple outbreaks that occur in small infection clusters with relatively low transmissibility, and thus are too weak to cause an epidemic. Still, subcritical transmission from stuttering chain data is vital for determining whether avian influenza is close to the threshold of R0 >1. In this presentation, we will explore two methods of estimating R0 using transmission chains and parameter estimation through data fitting.