Emmmmm in case you missed it, that was facetious or a case of sarcasm if you're not sure what that means.
I'm one of those with underlying health issues that are affected by this and have taken medical advice. I can guarantee I'm in the top end of those that are fully aware of the potential and what should be done to negate any effects.
But having said that, take a look at what I said and genuinely think about it. 500 to me is an awful lot of people even if outdoors, unless they are spread out evenly throughout a stadium for example and at a distance where the virus will not spread, generally accepted by medical experts and virologists, as being no closer than 1.5 metres and for no more than a few minutes. The virus can survive on many surfaces for several hours ranging from 2 to 12. Again looking at what I said, if )and I do mean "IF") 100 of that 500 were carriers without symptoms, would it not spread quickly? If those 400 became contaminated and went home to 4 each, then suddenly 2100 are now carriers.
In truth, in answer to your question, the only actual way to stop the spread is complete lockdown and isolation. That just is not practical or possible.