Mumbai's R-value, which reflects how rapidly the Covid-19 pandemic is spreading, increased to over 1 in September end, according to a study.

The Reproduction number or R refers to how many people an infected person infects on an average. In other words, it tells how 'efficiently' a virus is spreading.
An R-value smaller than 1 means the disease is spreading slowly. Conversely, if R is greater than 1, the number of infected people is increasing in each round - technically, this is what is called the epidemic phase.