Took the girls back to the vet this morning for follow ups. Also took a lovely bag o' poo to be investigated as they hadn't produced any while incarcerated.
They've both lost weight, but both had high normal temperatures. They are eating and behaving almost normally again, but still have five days of antibiotics to go.
During normal times, Sachi is the more demonstrative cat, but in times of stress, Kitsu becomes VelcroKitty. She's the more sensitive girl. She's sitting between the keyboard and my chest as I type this, demanding kisses and hugs.
Let's hope the PooReport sheds some light on just what caused the KittyContagion.