[AndrewM]

Originally Posted by bloopbloob

Those numbers are plenty high, possible exponential growth. Anything greater than 1 means it's spreading. That 1.4-2.5 would be it's effective reproduction number.

A population will rarely be totally susceptible to an infection in the real world. Some contacts will be immune. Therefore, not all contacts will become infected, and the average number of secondary cases per infectious case will be lower than the basic reproduction number. The effective reproductive number (R) is the average number of secondary cases per infectious case in a population made up of both susceptible and non-susceptible hosts. If R>1, the number of cases will increase, such as at the start of an epidemic. Where R=1, the disease is endemic, and where R<1 there will be a decline in the number of cases.

If R=2, that means if one contact infects 2, then 2 infect 4, then 4 infect 8. Not exponential, but growing linearly. If R>2, then it becomes exponential growth

Thanks for the clarification. Looks like 13 cities closed now. WHO hasn't declared a global emergency so hopefully that is a good sign.