Quote from IAAF doctor:
When speaking to the BBC after Van Niekerk’s 400m victory, Venning insisted that letting Makwala race would “risk many, many, many more athletes not competing†because of the “very infectious and very virulent†nature of the virus.
That was a lie, because he didn't even have the virus, and they had no evidence that he did at the time the statement was made. In fact there is no evidence that he ever had such a virus, and no evidence in retrospect.
Radcliffe asked whether blood tests could have been done, even though Venning explained that blood samples were not relevant.
Thus according to the IAAF physician, there was no point to any of the testing they did, and all of their diagnosing was wrong. Therefore, why was Makwala kept from competing? Perhaps this was done for political reasons, to help ensure a victory for South Africa.