Please consider keeping your cat indoors.  We used to let ours outside on our porch one in a while but then the outdoor cats in our neighborhood started dying.  We took one that had hung around our place foe a while to a vet (my stepdaughter) and she diagnosed it as having Feline Lukemia.  Since that time we have seen 3 more of the outdoor cats ....who were obviously ill....diie.  I was told that there are 3 deadly cat viruses (Feline Lukemia, Feline Imunodeficiency Virus, and Feline Infectious Peritonitis) going around and all have no treatments once the cat is infected.  Theere is a vaccine for the most common....Feline Lukemia.