I was tested for toxo and was negative as well, which I found really unusual as I have been a vet nurse for 5 years and handled many cats with toxoplasmosis and their litters!! But... no, negative. Which goes to show how hard it is to get anyway...
To get it from animals, they have to have the disease and they only secrete it 14 days after infection in their faeces. Then the spores take 24 hours to develop in the poo... so it is hard to get the perfect timing.

!!!BUT!!! That shouldn't stop you from being cautious!! I stopped cleaning litter trays and handling unknown cats as soon as I found out I was pregnant. DH has had to clean our own cats litter for the whole time, even though our cat doesn't have toxo and the only way for him to get it is eating rats or other animals faeces with it, and he doesn't go outside!
I should be more worried about our dogs licks than our cats litter tray...

So...be cautious, but don't think you can't handle your cat at all right now!

Christy