The difference between R naught and real-time transmission is that R naught is the estimate of the reproductive number at the beginning of the epidemic, while real-time transmission refers to the current rate of spread. In Hong Kong, the reproductive number is about 1, meaning one infected person spreads to one more. In America, the reproductive number in February was probably around 2, similar to China. Infections have been gradually growing over time, with tens of thousands of people now infected.