SCA in the collaborative trial was prepared from its individual ingredients. Both SCA media differ in their concentration of elective substances: SCA from the prestudy contains 1 g/l ammonium iron (III) citrate and 1 g/l Na2S2O5, and SCA from the collaborative trial contains 0.5 g/l of both compounds. Dilutions were made with reduced saline solution (RSS) containing NaCl (8 g/l) and cysteine–HCl (0.5 g/l).