Hyperthyroidism in Cats?

I can't seem to find what I need online so I was wondering if anyone knew some things about Hyperthyroidism? I am watching 4 cats for 2 weeks while there owner is on vacation and 2 of the 4 have Hyperthyroidism. I Have other cats the oldest cat I own is 1 yr the youngest is 3 mn. I was just wondering if this Hyperthyroidism thing spreads by touch or saliva? There cats are all 15 years but in there own area away from my cats. I was just wondering if I needed to change my clothes/shower or simply wash my hands after I pet there cats? I really do not know much about this disease but any info will be appreciated!