Cats rarely pose any health problems for humans. The key concern, which is usually blown out of any sensible proportion, is toxoplasmosis.

Healthy adults can have toxoplasmosis and experience mild flu like symptoms that go away without treatment in a few days.

The concern that folks panic over is for pregnant women. The risk is small, but toxoplasmosis can infect the unborn and do more damage than it would with an adult.

OK, so what can you do about the soil assuming the cysts are in it? Nothing.

If cats are going to continue to use the garden even if you could kill the cysts there would always be the risk of their being reintroduced. Additionally, we have no control over the wild creatures that consider our garden litterboxes like rabbits, squirrels, rats, mice, chipmunks, birds and all the other beasties out there. Every one of these wild creatures is capable of carrying pathogens which can cause problems for humans.

There is always the risk of soil born pathogens in our soil no matter how careful we are, no matter how healthy the soil is, regardless of whether cats poop in them.

So, evaluate the threat and respond accordingly. If you are pregnant or have a compromised immune system or simply like to play it extra safe then don't put your hands in the dirt, wear gloves. Be mindful to not put your hands to your face until you have washed up after being in the garden. Use a mulch to shield the edible plants from soil splashes that could place pathogens onto the plant part you are about to eat. Wash all garden produce well before consuming it.

Personally I don't do any of these things, I rather enjoy my hands in the dirt and adore nibbling while in the garden, but everyone has different opinions and different perceptions of the risks involved and different thresholds for what they consider acceptable risks.