I give it a 10.
My take on when people caught the disease:
Joe when he took his glove off down on the planet,
Sulu and Riley when they tried to stop Joe from suicide,
Kirk and Spock when they stopped Sulu's escapade on the Bridge.
Spock touches Chapel in Sick Bay but Spock had already nerve pinched Sulu a while back. Kirk gets belted by Spock in the Briefing Room but, again, Kirk was wrestling with a bare chested Sulu earlier in the story, too.