Factors that enhance the transmission of pathogens are poorly understood. We show that Vibrio cholerae shed in human 'rice-water' stools have a 10-fold lower oral infectious dose in an animal model than in vitro grown V. cholerae, which may aid in transmission during outbreaks. Furthermore, we identify a bacterial factor contributing to this enhanced infectivity: The achievement of a transient motile but chemotaxis-defective state upon shedding from humans. Rice-water stool V. cholerae have reduced levels of CheW-1, which is essential for chemotaxis, and were consequently shown to have a chemotaxis defect when tested in capillary assays. Through mutational analyses, such a state is known to enhance the infectivity of V. cholerae. This is the first report of a pathogen altering its chemotactic state in response to human infection in order to enhance its transmission.