Modelling pathogens/protozoa (Giardia)

I am struggling to find a state variable that would represent non-motile protozoans. What i require is to represent them would involve the transport, death/decay, sedimentation and resuspension. If one models them as generic constituent (coliform) then no resuspension is accounted for. If they are modelled as suspended solids then there is no decay/death. Is there any way to include both mechanisms?