After Puck sings "Fat Bottomed Girls" to Lauren in the choir room, Santana walks up to him and puts her left hand (pointing her index finger) directly in front of his face. In next immediate shot she is using her right hand.
During the performance of "When I Get You Alone," Kurt morosely leans against a mannequin as the rest of the group performs. The next shot ("Because you walk steady/Because you talk steady") shows him standing next to the mannequin with his arms folded.
The incubation period for mono is approximately six weeks, so neither one of them could have shown symptoms the same week as they acquired the germs.