Are they controlling for the fact that they are only testing over 55s in the WC?
There is an explanation on the mediahack website as to how the calculation has been done in the absence of direct access to sufficient data as well as how they compensate or allow for the incomplete nature of just about all the data available for SA.
I have posted that link before.
I have also validated their maths and it is pretty robust.
No one will ever be able to prove any of this stuff because we are unlikely ever to see the whole picture.
The next best source of Rt calculations is to look at the "official" NICD attempts but these run weeks behind reality making the calcs possibly more accurate but pretty useless from a forecasting point of view.
I have posted those links also before today.
In the end the precise value is much less important than the overall trends. The trends for WC is downwards. SA as a whole also trended downwards until the virus took off in EC and GP.
All this shows much as now happening in the USA, that ultimately nothing will stop this virus IF the population at large does not take responsibility for their own protection.
We know that virtually across the board, the SA population is just not bothered, some because they have no choice and others because they are just stupid and all sorts in between.