The Gunners played out a 1-1 draw with Bayern Munich in Shanghai on Wednesday before winning 3-2 on penalties.
Wenger told reporters: "We have a virus in the camp. The doctor thinks it is food poisoning.
"Mertesacker and Giroud were sick. Kolasinac was sick. Theo and Aaron have had a little bit of food poisoning as well. I don't know what they ate."
Arsenal move on to Beijing where they face Chelsea on Saturday in the fourth and final game of their tour.