I was thinking of building one symbiote as a Xenos Abomination and see what gang or cult comes into contact first if they defeat it then no symbiote infection crisis, but if they lose I'd snag a box of that gang or cult and build symbiote infected versions and slowly spread it like a plague.
I'd model them as if the symbiote is spreading across the body but not fully engulfing them.
I'd of course do a custom scenario for a rescue attempt to cleanse former gang members of the symbiote infection, but risk getting infected themselves.