Presence of pathogens without causing disease.
Of particular relevance is the potential for these assymptomatic pathogens, or pathogens otherwise acting like organisms, to be transmitted to new hosts where disease in fact may then occur. See more or less equivalently the concept of carriers or, especially, (or ).
For additional, historical discussion, see:
The carrier state is notably problematic with regard to strictly defining Koch's postulates, since unaffected also carry the presumptive disease-causing agent.