Not saying I know what particular method was in fact used… but ya do know even simple power mains can carry two way digital communications. Think of DSL over old fashioned powered Tip And Ring phone lines full internet simultaneous with phone conversation.
>>>“Something is certainly making some people sick, but what is it?”
Nocibo induced psychosomatic hypochondria. If you tell people all day everyday for weeks and months on end that the air is full of deadly pathogens… people will get sick from nothing more than the words into their heads. There need not be ANYTHING in the air. Please remember that.