Yes this is a risk, but in general pretty low if you know the person well. If you are taking the sample from your husband or wife you would hope you would know if they have HIV or not.

Actually the risk of getting worms is an interesting potential positive. There is a lot of data suggesting that the lack of intestinal worms in western countries is one of the reason for the rise of autoimmune diseases like Crohns. The theory is that the immune system in the gut is designed up to keep worms under control and in their absence starts attacking things like the gut tissue instead. There are a couple of stage three trial currently running that are giving people pig wipworms (they can infect but not reproduce in the human gut) to treat Crohns. The earlier trials were really encouraging so it will be interesting to see how they turn out.