Answer: You should probably wear gloves while working the soil and take care to clean up and remove the cat manure. Unless your vegetables have come in direct contact with the cat manure, the usual kitchen scrubbing routine should be sufficient. You can also dip your vegetables in a solution of water and ordinary household bleach, then rinse, to clean them more thoroughly.
Cats can be deterred in a number of ways, some more successful than others. There are commercially produced repellent sprays available specifically for cats, and you can try home-made repellents based on pepper and/or garlic. Some gardeners report that using one type of mulch or another seems less attractive to some cats, some report good results by covering the soil with wire mesh or screening, others report luck using thorny stems such as rose trimming sprinkled among the plants. A hose spray activated by motion detector might also work. Some have found success allowing a pet dog to patrol the area.
You might also try talking to the owners about the dangers of allowing their cats to roam. There may also be ordinances against allowing pets to wander. If these are stray cats you might contact the local animal control authorities.
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