Use the Big Head Mode and Big Head Enemies cards. If you only have the Big Head Mode card, which makes Lara's head big, it will add some amount of score bonus in Endurance mode because you will be easier to hit. However, the Infected here are melee-only, with an occasional suicide grenadier, so it will not be too difficult. Also, consider using the card that adds a 100% score bonus. It makes Infected only killable by headshots and finishers and will make sure that you get the correct kind of kill. You have approximately 12 seconds between each kill. Infected will spawn everywhere, especially if you make noise.