Acute illness from Campylobacter jejuni may require high doses while infection occurs at low doses.

•This study generalizes infection and illness dose response relations for Campylobacter jejuni, accounting for variation in pathogen (strain) and host (immunity, species) characteristics.•Susceptibility to infection likely is high, requiring small doses to colonize.•In outbreaks illness occurs at low doses, while in challenge studies high doses may be required.•This can be explained by selection bias: outbreaks select for highly virulent strains, not propagated in culture, and hosts susceptible to developing detectable symptoms of acute illness.•Nonhuman primates cannot be shown to have higher susceptibility to campylobacteriosis than humans.