The phrase "most infect" can be replaced with a variety of synonyms that effectively convey the same meaning. Some possible alternatives might include "highly contagious," "extremely infectious," "most transmissible," or "very communicable." Depending on the context in which the phrase is being used, additional options might include "very virulent," "most pathogenic," "extremely epidemic," or "most pandemic." Ultimately, the choice of synonym will depend on the specific tone and emphasis that the speaker or writer wants to convey, as well as the target audience and intended impact of the message.